Preheat the oven to 375 degrees F.
In a large bowl, combine the whole eggs, 1-cup milk, 3/4-cup flour, and a pinch of salt and pepper. Mix well with a whisk and set aside in the refrigerator for 30 minutes.
Meanwhile, in a medium stock pot, melt 5 tablespoons butter over medium-high heat. Whisk in the remaining 1/2-cup flour and cook over medium heat 5 minutes, whisking constantly.
In a separate pot, heat the remaining milk over medium heat until it is warm but not scalded. Slowly whisk the warm milk and the beaten egg yolks into the butter and flour mixture over medium heat, stirring constantly. Cook this mixture over medium heat, stirring, until it thickens to the consistency of chowder. Remove from heat and set aside.
Remove the crepe batter from the refrigerator and stir. Heat a non-stick pan over high heat and pour in enough of the batter to just coat the pan. Cook for 1 minute, then flip and cook for an additional minute. Set the crepe aside and continue with the remaining batter until it is all used up. Set aside.
In a 12 to 14-inch saute pan, heat the olive oil over high heat until hot but not smoking. Add the onion and cook for 2 minutes, until softened. Add the shrimp and cook until they are just pink, about 2 minutes. Add the prosecco and tomato puree and cook over high heat an additional 2 minutes. Season with salt and pepper, to taste, and remove from heat.
Lightly butter or grease a 10-inch round terracotta casserole and line the bottom with a few crepes. Spread about 1/3 cup of the bechamel over the crepes, then top with some of the shrimp. Repeat this layering process until all ingredients are used up. Top with the ricotta salata and bake, uncovered, for 20 minutes, until cheese is bubbling and bechamel has firmed into a custard-like consistency. Let cool 5 minutes before serving.