If your ricotta seems to have a lot of liquid, set it in a fine mesh strainer to drain off excess liquid about 30 minutes before you start cooking. If your ricotta seems fairly dry and compact, you can skip this step.

Whisk together flour, baking powder, sugar, and salt in a small bowl. Combine ricotta, milk, egg yolks, lemon juice and zest, and vanilla in a separate, larger mixing bowl. Add the dry ingredients to the ricotta and milk mixture, stirring gently until just combined.

Beat the egg whites in a mixer until stiff. Stir a small scoop of the egg whites into the pancake batter to lighten the batter, then fold in the remaining whites with a spatula.

Heat a griddle over medium-high heat. Brush a small amount of the melted butter over the pan (or you can just smear one end of a stick across the pan), just enough to coat the surface. Use a 1/4-cup measure to pour batter onto the hot griddle. Cook the pancakes for about 3 or 4 minutes, until the undersides are golden and you see a few bubbles popping through the pancakes. Flip the pancakes and cook another 2 minutes, until golden. Repeat with the remaining pancakes.

Serve the pancakes immediately, with maple syrup or lemon curd.