Prepare the Roof: In a medium, round pan, melt 2 cups of sugar over medium heat until golden brown. Carefully pour the caramelized sugar into the bottom of the pan, swirling to coat evenly.
Layer the Pineapple and Plums: Arrange the cooked pineapple slices over the caramel, placing a pitted black plum in the center of each slice. Set aside to cool.
Make the Cream: In a bowl, dissolve 2 tablespoons of cornstarch in 1/2 cup of milk. In a saucepan, combine the remaining milk, condensed milk, and sifted egg yolks. Heat until hot, then mix in the dissolved starch. Stir continuously until thickened, then remove from heat and let cool slightly before folding in the whey-free cream.
Combine and Chill: Pour the creamy mixture over the fruit layer in the pan.
Prepare the Sponge Cake: In a bowl, beat 4 egg whites until stiff peaks form; gradually add 6 tablespoons of sugar and continue beating until glossy. Gradually mix in 4 egg yolks, one by one. Gently fold in 6 tablespoons of wheat flour and 1 tablespoon of baking powder.
Bake the Cake: Carefully spread the sponge mixture over the cream layer in the pan. Bake in a preheated medium oven (around 350°F) until golden and a toothpick comes out clean.
Chill and Serve: Let the pie cool to room temperature before refrigerating until fully chilled. Serve the pie cold for a refreshing treat!