Preheat oven to 340F. Butter and flour a 10 inch springform pan.

Combine eggs, sugar, orange zest, vanilla extract, salt, and vanilla sugar in the bowl of a stand mixer (or use a hand mixer). Beat at medium-high speed for at least 15 minutes until the mixture is very pale and frothy and has some body to it.

Gently sift and fold in the flour a little bit at a time, making sure it is combined well. Try not to deflate the batter.

Pour the batter into the springform pan. Bake for 35- 40 minutes. Check the middle of the cake, turn off the oven, but leave the cake in the oven to cool gradually, with the oven door propped open.

Once the cake is cool. Invert it and take it out of the springform. Cut it into two layers. Pour orange juice over the cake layers.

If you are using whipped cream, use a spatula to spread some cream between the layers before reassembling the cake, then top with more whipped cream and orange zest (and flowers!).