Line a 6-inch (15-cm) springform pan with a parchment circle. Nestle a strip of parchment paper into the sides of the cake pan to form a collar.

Preheat the oven to 305°F (151°C) with a rack in the center.

Using a stand mixer (or hand mixer), beat the egg whites and cream of tartar on medium-high speed until foamy and opaque, a few minutes. Lower the speed to add the sugar in increments. Turn the speed back to medium-high and beat until glossy, tripled in volume, and stiff peaks form.

Add the egg yolks, 1 at a time, and beat until just combined.

Mix in the remaining sponge cake ingredients until well-combined, scraping down the sides of the bowl as needed.

Transfer to the prepared pan and bake for about 40 minutes. Insert a bamboo stick into the cake. If it comes out clean, the cake is ready.

Keep the oven running.

Take pan out of the oven. Remove the parchment paper allow the cake to cool completely on a wire rack.

Cut the cake in half, cross-wise. Cover and set aside one-half of the cake.

Line the springform pan with a parchment circle and collar again. Place the other half of the cake into the pan. Cover and set aside for now.

In a blender, blend together all the baked cheesecake ingredients until smooth and non-lumpy, scraping down the sides of the blender bowl as needed. Pour the batter into the prepared pan (with the cake layer on the bottom) and bake for 40 minutes. The center should be wobbly but not runny. Cool completely. (Note that you can pre-blend the cheesecake batter and refrigerate overnight or up to a day in advance.)

Combine all the ingredients in a microwave-safe bowl and microwave for 10 seconds. Mix to dissolve all the gelatin in the water. Pour over the top of the baked cheesecake layer and refrigerate. Meanwhile... (if you're tired at this point, you can make the next layer at a later time.)

Bloom the gelatin in 1 tablespoon of hot water and set aside.

Using a double-boiler, heat the egg, milk, and sugar. Mix until the sugar dissolves. (Eggs are pasteurized at 140F, temperatures higher than that will cook the egg.) Add the bloomed gelatin and mascarpone cheese and mix until combined. Remove from heat and cool completely.

In a stand mixer fitted with the whisk attachment (or with a hand mixer), whip the heavy cream until stiff peaks form. Reserve some of the whipped cream for coating the cake later. Fold the cheese mixture into the heavy cream gently, until well incorporated. Pour into the pan (topping the gelee layer). Smooth out the top of the cake, cover, and refrigerate for a few hours.

Turn the half of the sponge cake you had set aside earlier into crumbs. The easiest way to do this is to use a blender or food processor.

Remove the cake from the refrigerator and the cake pan. Remove all the parchment paper. Coat the cake with the reserved whipped cream, but leave the top uncoated. Pat on the cake crumbs to cover the sides of the cake entirely.

Sprinkle a layer of sugar on top of the cake. Burn the sugar layer with a blow torch to achieve a crème brûlée effect. (The top layer needs to be very cold in order for it not to melt, so freeze the cake for about 30 minutes before using the blow torch.)

Top with optional toppings, like fruits or garnish with gold flakes. Enjoy!