Separate eggs. Chill the egg whites. Wash the lemon with hot water, dry it and rub off half of the peel. Squeeze half a little.
Mix egg yolks with milk, lemon zest and vanilla flavor. Mix flour and baking powder, sieve and stir in with a whisk. There is relatively little dough that is not very runny. Only if it cannot be stirred, add a little more milk.
Beat the egg whites with a splash of lemon juice and salt until stiff. After about a minute, gradually stir in the sugar. The egg whites should be firm enough that you could tip it over without it running out of the container.
First, gently stir a spoonful of egg whites into the egg yolk mixture with a spatula or spoon. Gradually fold in the rest of the egg whites in portions (in about 5 steps). The batter should be light and not runny, more like some firm whipped cream.
Heat the butter in a non-stick pan on medium heat. Place 3 - 4 servings in the pan with plenty of space between them, as the pancakes will still spread a little. To do this, first take a spoonful of dough and then put one or two more spoons on top. Then cover the pan and bake the pancakes for about 6 minutes.
Then turn the pancakes very carefully (for example by hand) and add a tablespoon of water to the pan (not directly on the pancakes). Then bake the pancakes covered for 5 minutes and bake them a little longer with the stove switched off.
Note: The heat levels and times may vary depending on the stove. You shouldn`t keep checking, but the pancakes won`t die immediately if you lift the lid and look.
Finally, garnish the pancakes on a plate with berries, ice cream, sauce etc. as you like.