Using a long serrated knife, carefully cut the cooled sponge cake horizontally into three even layers.
Position the bottom layer on a cake round or serving plate.
Spread half of the pastry cream in an even thin layer over the bottom cake layer, leaving about ½-inch border around the edge.
Gently spread a thin layer of raspberry jam over the pastry cream.
120 g good quality raspberry jam
Place the second cake layer on top and press down gently.
Spread the remaining pastry cream evenly over the second layer.
Position the final cake layer on top, pressing down slightly.
Using an offset spatula, mound the stabilized whipped cream onto the top of the cake, forming a generous dome. The dome should be highest in the center of the cake.
Spread a thin layer of whipped cream around the sides of the cake to create a crumb coat.
Transfer the cake to the refrigerator for about 30 minutes to firm up the whipped cream dome.
On a surface dusted with powdered sugar, roll the green marzipan into a large circle about 16 inches in diameter and ⅛-inch thick.
Carefully lift the marzipan using a rolling pin and drape it over the domed cake. Gently smooth down the sides, working from the top to avoid creating air pockets or wrinkles.
Using a sharp knife, trim away excess marzipan around the bottom edge of the cake.
Place the marzipan rose on top of the marzipan at the center of the cake. Dust the top of the marzipan lightly with powdered sugar just before serving.
2 tablespoons powdered sugar