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 - homemade ricotta wont require this step.
Whisk together flour, baking powder, sugar, and salt in a small bowl. Combine ricotta, milk, egg yolks, 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 with a handheld electric mixer until stiff. Stir a small scoop of the egg whites into the pancake batter to lighten the batter, then fold in the remaining egg white with a spatula.
Heat a griddle over medium-high heat. Melt a small bit of butter in the pan, just enough to coat the surface. 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 to 3 minutes, until golden. Repeat with the remaining pancakes.
Serve the pancakes immediately, with maple syrup.