Combine 1 1/2 cups plus 2 tablespoons butter, sugar, and egg in a bowl; beat with an electric mixer until creamy. Beat in mashed egg yolks. Add flour, ground almonds, and lemon zest. Knead into a dough. Cover and refrigerate for 1 hour.
Preheat the oven to 400 degrees F (200 degrees C). Line a rimmed baking sheet with parchment paper.
Roll out 2/3 of the dough on a lightly floured surface into a rectangle the size of the baking sheet. Lay onto the prepared baking sheet. Roll remaining dough into finger-thick rolls. Press dough rolls onto the cake in a diamond-shaped pattern. Brush rolls with beaten egg.
Bake in the preheated oven until golden brown, 20 to 25 minutes.
Pour 1/4 cup water into a saucepan. Sprinkle gelatin powder on top. Let stand until softened, about 1 minute. Place over low heat; stir constantly until granules are completely dissolved, about 3 minutes.
Heat cherry and apricot preserves in 2 small pots over low heat until hot. Strain through a fine-mesh sieve. Mix half of the dissolved gelatin into each flavor. Alternate filling the diamond shapes of the cake with the 2 different flavors. Arrange sliced almonds and candied cherries into flower shapes on top.