To prepare the filling:

1. In a medium bowl, thoroughly whisk together 4 tablespoons of milk with the flour until smooth. Whisk in remaining milk.
2. Transfer the milk and flour mixture to a medium saucepan over medium heat. Bring to a simmer while whisking constantly. Heat until steam emerges from the mixture.
3. Remove from heat and allow to cool slightly.
4. Cover the mixture with plastic wrap directly touching the surface of the mixture. Cool for 30 minutes.
5. In the bowl of a stand mixer with a paddle attachment, combine butter, sugar, citrus oil and vanilla. Mix on high speed for 5 minutes.
6. Add the milk mixture, and beat until smooth, about 5 more minutes. Add ricotta cheese a tablespoon at a time.

To prepare the cake:

1. Preheat the oven with a rack in the middle position to 335 degrees F.
2. Line the bottom of three 9-inch round pans with parchment.
3. Whisk flour, cornstarch, baking powder and salt in a small bowl.
4. In a second small bowl, whisk the milk and vanilla.
5. In a stand mixer with a wire whip attachment, beat egg whites on high speed until stiff peaks form.
6. Drizzle 1 cup of sugar over the egg whites while continuing to mix on high speed.
7. Scoop the mixture into a large bowl, and set aside.
8. Clean the mixer bowl and attach the paddle attachment to the mixer. Cream butter with remaining 1 cup of sugar on low speed.
9. Add egg yolks one at a time. Mix on low speed until combined.
10. Alternatively add dry and wet ingredients, working in small batches.
11. Fold the meringue into the batter using a flexible spatula. Evenly distribute the batter into the prepared pans.
12. Bake for 24 to 30 minutes until a cake tester comes out clean.
13. Cool the cakes for 5 minutes.
14. Run an offset spatula around the edges. Carefully invert the cakes onto a flat surface.

Finishing touches:

1. Lay down the first cake as a base layer.
2. Spread 1 cup of fresh strawberries and 1 cup of filling on top.
3. Add the second cake to sandwich the filling.
4. Spread 1 cup of fresh strawberries and 1 cup of filling on top.
5. Add the third cake with its flattest side facing up.
6. In the bowl of a stand mixer fitted with a whisk attachment, add heavy cream. Mix on high speed. Add sugar and vanilla extract. Whip until stiff peaks form.
7. Cover the entire outside of the cake with the whipped cream.
8. Add halved fresh strawberries around the base of the cake for a decorative touch.