For the spring tart, preheat the oven to 175 to 200 °C. Melt the butter and allow to cool.
For the dough, beat the egg yolks, sugar, grated lemon zest and lukewarm water until creamy. Whip the egg whites with the salt until very stiff.
Pile the snow on top of the egg yolk mixture. Sift the flour and cornstarch over it and fold it in. Gently stir the melted butter into the batter.
Grease the cake springform pan and dust with flour. Pour in the batter and smooth out, bake for 35 to 45 minutes. Make the proofing. Remove the cake from the pan and let it cool.
Cut the sponge cake dough once diagonally. Drizzle both bottoms evenly with liqueur. Spread the bottom part with the smooth jam. Place the top cake layer on top and press lightly until smooth.
For the icing, mix the powdered sugar with enough lemon juice to achieve a thick consistency. Coat the cake with it all around, smooth it out and let it dry.
For the decoration, first form a small piping bag. With the liquid chocolate icing in it, draw stems and a pattern around the edge (in the shape of U’s lined up, open towards the center of the cake) on the cake.
Then form the flowers from the candied violet and rose petals. Finally, using the pistachios cut in half lengthwise, place the leaves on top and decorate the edge. Refrigerate the spring cake.