Preheat oven to 350 degrees F. Spray three 13x9 inch or 11x9 inch pans with cooking spray and line with parchment paper.
In the bowl of a stand mixer using the whisk attachment, beat the eggs until thick and foamy (about 3 minutes). Pour them in a separate bowl, then add the sugar and the grated almond paste to the stand mixing bowl and beat until well-combined using the paddle. Beat in the butter, then beat in the already-beaten eggs. Continue beating as you add the almond extract and salt. With mixer on low (or by hand) gently stir in the flour.
Evenly distribute batter between 3 medium bowls. If you have a scale, weigh the total amount of batter and divide it into three equal bowls. Mix red food coloring into one, green food coloring into another, and yellow into another. Spread batter evenly across the parchment lined pans. The batter is thick and this task is kind of a challenge. I used a rubber scraper. Bake for 10-14 minutes or until a toothpick inserted in the center comes out clean. Let cakes cool completely on a wire rack.
When layers are cool, carefully loosen from pans and lift out by grasping parchment. Transfer the green layer to a large sheet of plastic wrap. Spread the green layer (top) with preserves. Top it with the yellow layer and spread yellow layer with preserves. Cap with pink layer. Wrap the plastic wrap around the stack of cakes and put the stack in one of the original pans. Put the stack in freezer. Note: Most recipes say to weigh down the layers, but I never weighed them down. Freeze until ready to use.
On or before the day you plan to serve the bars, remove the frozen cakes from the freezer. Place on a large cutting board and slice frozen cakes into bars the size of a butter stick – about 1 inch wide and 4 1/2 inches long. Trip the edges before or after slicing. If you plan on dipping, it's best to trim just the short sides of the rectangle and keep the long sides of the rectangle raggedy so that you'll have a longer handle for dipping. You're going to trim those anyway.
Keep the sticks frozen as you melt the chocolate.
Melt the butter in the microwave. Add the chopped chocolate to the melted butter and stir well. Return to microwave and microwave at 50% power for 30 second intervals, stirring at each interval until chocolate is melted and smooth. I did this all in a 2 cup Pyrex measure in smal batches – 3 oz of chocolate to 1 1/2 oz butter.
You can dip the cake sticks in the melted chocolate if it’s thin enough (which will depend on which brand of chocolate you use and how much you heated it) or you can just use a silicone pastry brush and just paint the chocolate coating all over the sticks and let it set. If it looks messy, coat with chocolate sprinkles – the kind called "Jimmie's" which are softer and less annoying than crunchy sprinkles.
Once your cake sticks are coated with chocolate and set, trim the raggedy ends and cut into about 4 neat squares.
I kind of lost track of yields, but if you figure you get 18 butter stick size cake sticks from an 11x9 inch pan and cut each into 3 pieces (minus the trimmings), you should get at least 54 nice size squares.