Preheat the oven to 400°F (205°C). Prepare a 9-inch springform pan by greasing with butter and dusting with flour. Have two 10-inch cardboard circles ready.

In a clean bowl, beat egg whites until frothy, then gradually add 1 cup sugar while beating until soft peaks form.

In a separate bowl, mix egg yolks, milk, lemon zest, salt, and vanilla extract until lighter in color. Fold this into the egg whites. Sift flour over the mixture and fold gently.

Spread 1 1/3 cups of batter into the greased pan and bake for 5-9 minutes until brown spots appear. Remove and cool; repeat for 7 layers.

To make the chocolate buttercream, beat butter and cocoa together until fluffy. Gradually add milk, vanilla, and confectioners' sugar until smooth.

Layer the cake: alternately stack cake layers with buttercream, reserving one layer. Chill for 6 hours.

For the caramel topping, melt sugar in a skillet over medium heat until amber-colored. Pour over the reserved cake layer and score into wedges while soft.