I’d never heard the term traybake until I started watching “The Great British Baking Show.” The Collins English Dictionary defines the term as “a flat, usually chewy cake which is baked in a tray, cut into small squares and served as a biscuit.” For the uninitiated American, that may need a bit of interpretation, as well. A tray, in this case, is a shallow baking pan, and a biscuit is what we would call a cookie. So a traybake is a cake disguised as a cookie, or perhaps a cookie disguised as a cake.
Here in the U.S., we might refer to a traybake as “bars” or “squares.” I found a brief history of “squares” on CooksInfo.com. It explains that recipes for squares in North America generally predate traybakes in the U.K. by several decades. Most recipes for squares appeared from the early 1900s to the 1950s. They tend to fall under the category of “comfort desserts” and often appear at community social events (think potlucks) because they (a) travel well, (b) feed a crowd and (c) can usually be eaten as finger food. An interesting side note: While in the U.S. an individual piece is called a bar or square, in the U.K, a piece of a traybake is usually called a slice.
Now that we’ve had our cultural lesson for the day, let’s get on with the bake. The challenge for this episode was to produce a traybake with layers of complementary flavors and good textures, each element made from scratch, and cut into identically sized squares or rectangles. It could be biscuit-, cake- or pastry-based.
I chose a pastry-based recipe, a rhubarb frangipane tart. The rhubarb in my garden is just ripe enough to start using it, and I’ve been wanting to try one of those fancy rhubarb patterns I’ve seen on the internet, like this one or this one. Unfortunately, I couldn’t get enough stalks that were exactly the same size, so I ended up going with a simpler design, based on this one.
I had some shortbread dough left over from my Bakewell tart petits fours, so I decided to use that as the pastry base, which I blind-baked before adding a layer of rhubarb puree. I made the puree with some rhubarb that I still had in the freezer from last year. The recipe for puree comes from a rhubarb ripple coffee cake that I’ve made many times. I covered the puree with a layer of frangipane, using the same recipe as in my Bakewell tarts, except instead of almond extract I added the zest of an orange to flavor it.
“Docking” just means pricking the dough with a fork. You can get creative here and make designs if you want. 
Blind bake the pastry until dry and lightly browned. Then remove the excess edges with a sharp knife or your hand. 
After letting the pastry shell cool, I spread on a layer of puree, then added a layer of frangipane.
I arranged the rhubarb on top of the frangipane in a chevron pattern. I hope to work up to some of the more complicated patterns, but this one was challenging enough for a first-timer. It’s all about getting uniform-sized pieces and keeping the angle of the cuts the same. Also, since my rhubarb is not as red as some that you see in pictures, I used an apple-jelly glaze tinted with a little red food coloring to give it a rosy glow.
Once the traybake was out of the oven and cooled, I cut it into squares, er, slices. Because I cut them along the lines made by the chevrons, they were not very uniform, something Paul and Mary would have remarked on, I’m sure. I decorated my squares with mascarpone whipped cream scented with orange blossom water and topped that with a raspberry and a thin slice of orange peel, which I curled around a bamboo skewer.
I was pleased with the flavors. (My husband gave it two thumbs up.) But I’m trying to figure out if my frangipane was underdone. Should it be more custard-y or cake-y? I’ve heard frangipane described as a pastry cream, but I’ve also had it in Bakewell tarts where it was more cakelike. If anyone can answer that question for me, I’d appreciate it!
Rhubarb Frangipane Tart
Rhubarb puree adapted from RecipeGoldMine.com
Frangipane adapted from TheSpruceEats.com
For the pastry shell:
- ½ c. unsalted butter, softened
- ¼ c. superfine (baker’s) sugar
- 1 c. + 2½ T. all-purpose flour
- 3½ T. cornstarch
- ¾ t. almond extract
For the rhubarb puree layer:
For the frangipane and rhubarb layer:
For topping:
Orange peel (optional)
Directions
- Line a square or rectangular tart pan (mine is 6 inches by 14¼ inches) with parchment paper.
- To make the pastry dough, place butter and salt into a mixer bowl and, using a paddle attachment, mix on medium speed until creamy, about 2-4 minutes. Add sugar and almond extract, and mix until well blended and the mixture is nice and creamy, about 1-2 minutes. Add flour and cornstarch, and mix on low speed until the flour is mixed in and the dough forms clumps. DO NOT OVERMIX. Using floured hands or a spatula, bring the dough together to form a cohesive ball, then turn it out onto a flat surface and flatten dough into a disk shape.
- Transfer the dough to a gallon-size zip-lock bag, but don’t close the bag. On a flat, smooth surface, use a rolling pin to gently roll the dough to about a ½-inch thickness. (Keeping the bag open will allow excess air to escape so you can roll the dough out without the bag exploding.) Once the dough is ½-inch thick, seal the bag and place it on a baking sheet in the refrigerator. Leave to chill for 30-60 minutes, or until the dough is firm.
- While dough is chilling, make the puree. Place the rhubarb in a 1½-quart, heavy-bottomed saucepan. Toss with sugar and cornstarch. Cook on low heat, covered, for about 5 minutes. Remove the cover, and cook on medium-low heat to cook down the fruit, stirring occasionally, about 10 to 15 minutes, until the fruit is very soft, and the sauce is smooth and thickened. If it still seems too chunky, you can puree it with an immersion blender or in a traditional blender. Let cool and, If desired, tint with a few drops of red food coloring.
- Preheat oven to 400°F. Remove pastry dough from the fridge and carefully take it out of the zip-lock bag. Place flattened dough on parchment paper on a smooth surface, and roll it to a thickness of about ¼ inch and about 2 inches longer and 2 inches wider than your tart pan. (NOTE: As you can see in my photos, I did not roll mine long enough to cover the ends of the tart pan. This was because I was using leftover dough and didn’t have quite enough. I solved this problem after baking the tart by cutting off the ends so I didn’t have any corner pieces.) Transfer to the tart pan, using your fingers or a small ball of dough to press the pastry gently into the corners of the pan. If the dough cracks, press the cracks together with your finger, or press a small piece of dough into the crack. Leave extra dough hanging over the edges of the pan.
- Dock the pastry with a fork. Place the tart pan on a cookie sheet and refrigerate for another 30-60 minutes, until well chilled and stiff. Place a piece of foil or crumpled parchment paper inside the tart pan and fill it with dried beans or rice. Blind-bake the pastry for 10 minutes or until the foil comes away from the pastry shell without sticking. After removing the foil and beans from the partially baked shell, return it to the oven for another 10 minutes or until it is dry and just beginning to show some color. Reduce oven temperature to 350°F.
- Place tart pan on a cooling rack and allow to cool while you make the frangipane. Use a sharp knife or the heel of your hand to trim the pastry so it is level with the edge of the pan.
- To make the frangipane, cream butter and sugar together with an electric mixer. Add almond meal and mix to combine, then add the egg and orange zest, gently beating until well mixed. Add flour and mix well.
- Spread a thick layer of puree in the bottom of the cooled pastry shell. (You may not need all of it. Leftover puree can be stored in the fridge for about a week or frozen for several months.) Spread the frangipane on top of the puree.
- Cut the rhubarb into equal-sized pieces, cutting at an angle to the edge of the stalk, rather than perpendicular. Arrange in a chevron pattern on top of the frangipane, as shown here: https://images.app.goo.gl/JSwqQrvkwRk8v88z6. (If some pieces are too thick, try cutting them in half lengthwise.) Sprinkle with superfine sugar.
- Bake at 350°F for 30 minutes or until the frangipane is set and nicely browned. Remove from oven and place on baking rack to cool.
- Melt the apple jelly in the microwave and add a few drops of food coloring, if desired. Brush hot jam evenly over rhubarb. When tart is completely cooled, remove from pan and cut into 9 or 10 equal squares (or slices).
- Using a whisk attachment on an electric mixer, whip the mascarpone with the powdered sugar until light and fluffy. Add whipping cream and whip until stiff peaks form. Transfer to a piping bag fitted with a star tip, and pipe a single dollop of cream onto each bar. Top each with a raspberry and a thin curl of orange peel, if desired. Serve immediately or refrigerate until serving.
Here's the Dish 