In a large bowl, combine the ricotta, eggs, milk, vanilla, lemon zest and juice, butter, and sugar. Whisk together until smooth and you have broken up any lumps of ricotta.
In a medium bowl, mix the flour, baking powder, and salt together, then add to the ricotta mixture. Switch your whisk for a rubber spatula and mix the dry ingredients in until you have a uniform batter.
Heat a large nonstick skillet over medium heat. Add a knob of butter. Once it has melted, scoop about ¼ cup of batter and pour it into the pan. Depending on the size of your pan, you should be able to fit about three pancakes in the pan at a time.
After 4 or 5 minutes, when the edges are browned and little bubbles have formed on the surface, flip the pancakes and cook for about another 2 minutes, until golden. Transfer the pancakes to a cooling rack and allow to cool to room temperature before packing.