Rainbow Cookies Meet Crumb Cake

Directions

1. Make the batter. Heat the oven to 350°F with a rack positioned in the center. Spray a 9x9-inch metal cake pan with cooking spray, then line with parchment paper, leaving an overhang on 2 sides. (If you happen to have 3 pans, position oven racks in the upper and lower third.)
2. Place the egg whites and a pinch of salt in a very clean bowl of a stand mixer or large bowl. Using the stand mixer’s whisk attachment or an electric mixer, beat the egg whites on medium-high speed until the mixture forms soft peaks, 4-5 minutes. With the mixer running, slowly add ¼ cup (50 grams) of the sugar in a steady stream, then increase the speed to high and beat until the mixture forms stiff, glossy peaks, 7-9 minutes. Transfer to a medium bowl.
3. In the same bowl (no need to clean it), combine the butter, almond paste, remaining ¼ cup (50 grams) sugar, ¾ teaspoon salt, and extracts. Switch to the stand mixer’s paddle attachment (or keep using the electric mixer) on medium-high speed until light and creamy, scraping down the sides of the bowl as needed (you might find there are a few little lumps of almond paste in the batter—this is okay), 7-10 minutes. Beat in the egg yolks on medium-high speed until totally combined. Scrape down the sides of the bowl, then beat in the flour on low speed until just incorporated.
4. Transfer about one-quarter of the egg white mixture into the cake batter and use a flexible spatula to fold the mixture together until just combined. Fold in the remaining egg white mixture in 2 additions until barely combined—there can be streaks of egg white (don’t worry, you’re about to mix this batter more).
5. Divide two-thirds of the batter evenly between 2 medium bowls (leaving the remaining third of the batter in the original bowl—each bowl should have about 295 grams of batter). Mix the red food coloring into one bowl and the green food coloring into another. You can use less dye for more pastel cookies; the more dye, the more richly saturated the baked cookie color, but the baked cakes will be more pale than the batter.
6. Scrape one bowl’s batter into the prepared pan and smooth into an even layer with an offset spatula. (If using 3 pans, fill all of them) Bake for 8 to 10 minutes, until dry to the touch and starting to pull away from the edges of the pan. (If using 3 pans, place divide the pans between both racks and switch their positions halfway through.) Let cool for 5 minutes, then lift the cake from the pan with the parchment edges and transfer to a wire rack to cool completely. Re-grease the pan and line with fresh parchment (or peel off and reuse the parchment from the cake) and repeat with the next 2 batches of batter.
7. Once the cakes have cooled completely, line a sheet pan with a sheet of plastic wrap and a piece of waxed paper. Remove the parchment and place the green cake layer into the center of the pan, then spread with half (85 grams) of the jam. Gently place the white cake layer over the jam, then spread on the remaining jam. Place the red cake layer on top, then wrap the cake in the waxed paper and plastic wrap. Transfer to the refrigerator on the sheet pan. Weigh down the cake by filling the 9x9 pan with a few cans and placing directly on top of the wrapped cake (you can also just place a heavy skillet on top). Refrigerate for at least 4 hours or up to 24.
8. Make the crumb topping. Heat the oven to 300°F. In a medium bowl, use a fork to mix together the flour, sugar, baking powder, cinnamon (if using), and salt. Gently mix in the butter until the mixture forms large crumbs. Use your hands to scoop up big chunks of crumb topping, then crumble with your fingers directly onto a parchment-lined sheet pan. Bake for about 15 minutes, until barely firm, then let cool completely in the pan.
9. Assemble the cookies. Melt the chocolate in the microwave or over a double boiler. Unwrap the chilled cake and transfer with the waxed paper to a cutting board. Using an offset spatula, spread a scant half (63 grams) of the melted chocolate over the top of the cake (don’t worry about evenly spreading over the edges, they’ll be trimmed). Transfer to the refrigerator and chill, uncovered, until the chocolate sets, about 30 minutes. Carefully flip over the cake, and spread the remaining melted chocolate over the surface. Immediately press the crumb topping evenly over the top, breaking up the crumbs into smaller pieces as you crumble. Sprinkle the flaky salt and sprinkles (if using) over the crumble. Let set for 5 minutes at room temperature. Use a large knife to trim the edges, then slice into 1x1½-inch pieces. Return to the refrigerator and chill for another 30 minutes. Once set, serve or store in an airtight container between layers of waxed paper, if layering. Cookies can be frozen in an airtight container for up to 3 months.