Preheat oven to 350°F. Grease and line three 9" x 13" sheet pans with parchment and cooking spray.

Beat Almond Paste (grated using large hole side of a box grater) and sugar in mixing bowl until the texture of sand (a food processor makes short work of this step and then add to mixing bowl). Add butter and beat until light colored and smooth.

Add eggs one at a time, beating well between each, until light and fluffy.

Sift flour and salt into almond mixture. Beat on low until just incorporated. Divide batter into thirds (1 cup plus 1 tablespoon for each bowl).

Add 10 drops green food coloring to one bowl, 10 drops yellow food coloring into another and 10 drops red food coloring into last bowl. Mix each batter until color is well blended.

Add batters to prepared pans, spreading evenly to edges. A thin metal spatula works well for this step.

Bake all three pans together, unless oven is too small, in that case bake in batches. Bake for 10-12 minutes or until edges are golden and toothpick inserted in middle comes out clean.

Cool pans on wire rack for 10 minutes. Loosen cake edges from pan, with a thin knife, and invert onto rack. Gently peel off parchment and cool completely.

Lay parchment on a flat surface that will fit in refrigerator. Place green cake on top of parchment. Spread top with ⅓ cup jam. Top green layer with yellow cake. Spread top with remaining jam.

Top yellow layer with pinkish-red cake. Cover with parchment and weight top with a book. Chill in refrigerator for 2 hours.

Set a stainless steel bowl over a pot of barely simmering water. Add chocolate and shortening and stir until melted.

Remove cake from refrigerator. Evenly spread top (not sides) with chocolate. Let stand at room temperature until chocolate is set.

To serve, trim edges with a sharp knife. Cut into small squares (6 rows across and 6 rows down) and for diamonds (6 rows across and 1-inch diagonal rows). Refrigerate cookies in an airtight container in single layers for up to one week.