Step 1: Make the Sponge Cake

1. Preheat oven to 350°F (175°C). Grease and line an 8-inch round cake pan.
2. In a mixing bowl, beat eggs and sugar until light and fluffy (about 5 minutes).
3. Sift together flour, baking powder, and salt. Gently fold into the egg mixture.
4. Stir in melted butter and vanilla extract.
5. Pour batter into the prepared pan and bake for 25–30 minutes until golden.
6. Let cool completely before slicing into three equal layers.

Step 2: Prepare the Custard

1. In a saucepan, heat milk until warm (do not boil).
2. In a separate bowl, whisk egg yolks, sugar, and cornstarch. Slowly add warm milk while whisking.
3. Return mixture to the stove and cook on medium heat, stirring constantly, until thickened.
4. Remove from heat, add vanilla and butter, and let cool completely.

Step 3: Whip the Cream

1. In a chilled bowl, beat heavy cream, powdered sugar, and vanilla until stiff peaks form.

Step 4: Assemble the Cake

1. Place the first sponge layer on a serving plate. Spread a layer of custard.
2. Add the second sponge layer and spread a thick layer of whipped cream.
3. Place the final sponge layer on top and cover the entire cake with the remaining whipped cream, forming a dome shape.

Step 5: Cover with Marzipan

1. Knead marzipan with green food coloring until evenly colored.
2. Roll out marzipan into a thin circle (large enough to cover the cake).
3. Carefully drape marzipan over the cake and smooth it down. Trim any excess.

Step 6: Decorate and Serve

1. Dust with powdered sugar and top with a marzipan rose if desired.
2. Slice and enjoy your authentic Swedish Princess Cake!