1. Place butter and milk in a small saucepan over medium-low heat, stirring occasionally until butter has melted; remove from heat and let cool slightly.
2. In a medium bowl, sift together flour, baking powder, and 1/2 teaspoon of the salt.
3. Whisk together egg yolks, 1 tablespoon of the sugar, lemon zest, and vanilla in a large bowl. Mix in a quarter of the milk-butter mixture, then add in the remaining milk-butter mixture until smooth.
4. Add the reserved flour mixture and stir with a rubber spatula until just combined.
5. In a medium bowl, whisk egg whites to soft peaks. Halfway through whisking them, sprinkle in the remaining 1 tablespoon sugar and 1/2 teaspoon salt. Using the rubber spatula, fold the whites into the reserved batter until just combined.
6. Gently fold the ricotta into the batter until the mixture is lumpy and streaked with ricotta.
7. Heat a large nonstick frying pan, griddle, or seasoned cast iron skillet over medium heat until hot, about 4 minutes. Lightly coat the pan’s surface with butter, then use a 1/4-cup measure to scoop the batter into the pan. Cook until bubbles form on top of the pancakes, about 4 to 5 minutes.
8. Flip and cook the other side until the bottoms are golden brown, about 1 to 2 minutes more. Repeat with the remaining batter. Serve immediately with powdered sugar, fruit, butter, or maple syrup.