In a large mixing bowl, combine the ricotta cheese, egg yolk, milk, lemon zest, and lemon juice. Mix until well combined.
In another bowl, sift together the flour, baking powder, sugar, and salt.
Gradually add the dry ingredients to the ricotta mixture, stirring gently until just combined.
In a separate bowl, beat the egg white until stiff peaks form. Gently fold it into the pancake batter.
Heat a non-stick skillet over medium heat and lightly grease it with some of the melted butter.
Pour about 1/4 cup of batter onto the skillet for each pancake. Cook until bubbles form on the surface and the edges look set, then flip and cook until golden brown, about 2-3 minutes per side.
Serve the pancakes warm, with your choice of toppings such as fresh berries, maple syrup, or additional lemon zest.