1. Place the eggs and sugar in the mixer bowl and beat until they become fluffy, pale, and double in volume.
2. Add the milk and cognac, then take it off the mixer. Add the flour, baking powder, and vanilla, gently folding with a spatula (rubber scraper).
3. Be careful not to let the air escape. Pour the mixture into a rectangular baking pan lined with non-stick parchment paper and bake in a preheated oven at 180°C for 35-40 minutes.
4. If you prefer, you can bake the sponge cake in smaller trays and make various cakes.
5. When the sponge cake cools, cut it and sprinkle it with syrup from preserved mandarin and a little rose water, or whatever sweet syrup you have on hand (citrus syrup works best).
For the Rose Cream:
1. Dissolve the 1 cup of rose syrup in water (to have a total of 1 liter). Take a little of the mixture into a bowl and add the cornstarch. Stir until dissolved.
2. Put the remaining rose syrup mixture on the heat, and when it gets warm, pour in the cornstarch mixture. Stir until it thickens, lower the heat, and stir for 1-2 minutes.
3. Place a piece of sponge cake, which you have sprinkled with syrup and a little rose water, on the bottom of a glass baking dish. Pour the rose cream over it. Cover with another piece of sponge cake and sprinkle with syrup and rose water.
For the Mandarin Cream:
1. In a saucepan, pour 3 cups of mandarin juice and the sugar. Heat until it boils. In a bowl, put the remaining mandarin juice (1 cup) and dissolve the cornstarch.
2. Pour this into the hot mandarin juice and stir until the cream thickens. Add the mandarin zest and stir.
3. Place the mandarin cream on top of the sponge cake layer and let it cool. Decorate with candied mandarin peel and dried rose petals.
