Whisk flour, sugar, baking powder and salt in a bowl. In a second bowl whisk egg yolks, ricotta, milk, lemon zest, lemon juice, vanilla and melted butter. Small ricotta curds are fine; the mixture need not be completely smooth.

In a clean bowl beat egg whites until soft peaks bend at their tips. Stir the flour mixture into the ricotta mixture just until the dry patches disappear. Fold in the whites in two additions with a spatula; do not beat out all the air.

Heat a large nonstick skillet or griddle over medium-low heat. Brush with a thin film of oil. Drop a small test spoonful of batter; it should sizzle gently without browning immediately. Adjust the heat before cooking full pancakes.

Scoop twelve pancakes using about 1/4 cup batter each, working in batches with space to spread. Cook 3–4 minutes on the first side, until edges look set and the underside is golden. These moist pancakes may show fewer surface bubbles than standard pancakes.

Flip once and cook 2–3 minutes, until the centers spring back and no wet batter remains when a test pancake is cut. Keep cooked pancakes on a rack in a 200°F (95°C) oven briefly while finishing the batches. Serve three pancakes per person; toppings are extra.