This fluffy, versatile layered sheet cake can be easily turned into a spectacular dessert by filling it with Chantilly cream and fresh fruits. It's a cake for any and every occasion, from birthdays to just-because.
In a large mixing bowl, sift the flour, baking powder, and salt, then whisk to mix the dry ingredients together. Set aside.
In the bowl of a stand mixer fitted with the whisk attachment (or in a large mixing bowl, if using a handheld mixer), beat the egg yolks and sugar together until the mixture is pale and fluffy and falls from the beater in ribbons, 1 to 2 minutes. Scrape down the bowl, then add the milk and vanilla and whisk to incorporate. Add the dry ingredients and fold with a spatula to incorporate.
In a clean bowl, beat the egg whites until soft peaks form. Transfer the beaten egg whites to the bowl with the cake mixture, then gently fold to incorporate.
Pour the batter into the prepared baking sheet and even out the using a spatula. Bake for about 18 minutes, or until light golden brown and a toothpick inserted in the center each cake comes out clean. Transfer to a wire rack and let cool to room temperature.
While the cake cools, prepare the Chantilly cream filling: Pour the heavy cream in a large mixing bowl, then add the powdered sugar and vanilla extract. Beat until soft peaks form, about 3 to 5 minutes. Cover the bowl with plastic wrap and refrigerate until needed.
Unmold the cake: slide a sharp knife all around the edge of the pan, then use a spatula to help you lift the cake out of the pan. Invert to a large cutting board. Using a serrated knife, slice off the uneven edges of the cake (these make a great snack!), then slice the cake in two to create two even rectangles (each rectangle should measure about 12 x 8 inches / 30 x 20 cm).
Prepare the fruit filling: Measure out half of the fruits (keep the remaining half to use as topping). If using berries, transfer to a shallow bowl and roughly mash the fruits with a fork so they break down a bit and release some of their juices. Mix in the sugar and flavoring of your choice. If using stone fruits, dice the sliced fruits, then transfer to a shallow bowl and roughly mash the fruits with a fork so they break down a bit and release some of their juices. Mix in the sugar and flavoring of your choice. (It’s best to prepare the fruits right before assembling the cake because they will keep on releasing juices upon sitting.)
To assemble the cake: Set one of the cake rectangles on a large serving plate, a baking sheet covered with parchment paper, or a cutting board. Cover with half of the Chantilly cream, then spoon the mashed fruit filling over the cream. Cover with the second cake rectangle. Slather on the remaining Chantilly cream, then top with the reserved fresh fruit and garnish of your choice.
Serve immediately, or refrigerate for up to two hours before serving. This cake is best enjoyed the day it is made.