Measure milk into a liquid measuring cup and add butter. Microwave for about 30 seconds, or until butter is melted. Stir well and set aside to cool.
In a small bowl, sift together flour, baking powder, and salt; set aside.
Place egg yolks, sugar, lemon zest, and vanilla in a separate large bowl and whisk to combine.
Stir the cooled milk/butter mixture into the sugar/egg yolk mixture. Then stir in the dry ingredients and stir just until combined (don't over mix!) Gently fold the ricotta into the batter, again being careful not to over mix.
In a medium bowl, whisk the egg whites until soft peaks form. Gently fold the egg whites into the batter, just until combined.
Heat a griddle or large nonstick frying pan over medium heat. Once hot, grease the pan with butter or cooking spray and spoon 1/4 cupfuls of batter onto the pan, spreading batter into an even layer. Cook until bubbles form on top, then flip and cook until golden and cooked through.
Serve with freshly strawberries and a dusting of powdered sugar, if desired.
Freezing Instructions: Allow pancakes to cool completely. Place on a baking sheet and flash freeze for 30 minutes (so they don't stick together). Place in a freezer bag and freeze for up to 3 months. Reheat in the microwave.Recipe adapted from Chow.