Preheat your oven to 350 F degrees. Grease the bottoms of 3 matching 13x9-in. baking pans (also called jelly roll pans) (or reuse 1 pan). Line the pans with parchment paper; grease the paper.
In a large mixing bowl, break up the almond paste with a fork. Add the butter, sugar, and egg yolks. Beat on medium until light and fluffy, 5-7 minutes. Use the paddle attachment if using a stand mixer.
Stir in flour, salt, and cornstarch together. Slowly add to the almond paste mixture
In a clean bowl, beat egg whites until soft peaks form. Use clean beaters or whisk attachment. Gently fold into dough, mixing until thoroughly blended.
Divide batter into 3 equal portions. Color 1 portion with red food coloring, 1 with green and leave the remaining portion to stay white. Spread each portion into the prepared pans, one for each color. Let the batter rest for 10 minutes.
Bake until the edges are light golden brown, approximately 10 minutes. Cool in the pans for 5 minutes, then invert onto wire racks; remove the paper. Cool completely.
Assembly
Place a piece of parchment paper on a large baking sheet. Place the green layer on the paper. Spread evenly with raspberry jam. Top with white layer and spread with apricot jam. Top with the red layer.
Cover the top with plastic wrap. Place a cutting board or another sheet pan on top. Top with something heavy like a skillet or a few cans to compress layers. Refrigerate for at least 4 hours or overnight.
Once the cake is chilled, melt chocolate and cream in a microwave safe bowl or a small sauce pan. Stir frequently.
Pour the chocolate ganache over the chilled cookies and spread out. Don't worry if it drips off the sides. Refrigerate for 30 minutes until the chocolate is set.
With a sharp knife, trim edges. Cut into ½-in. strips across the width; then cut each strip into 4-5 pieces. Store in airtight containers.
Notes
This recipe can be made in 3 separate pans, or you can reuse the same pan 3 times.
Heat the jam in a microwave-safe bowl for 20 seconds to make spreading easier.
You can use chocolate ganache instead of semi-sweet chips if a smoother look is desired.