Sift the flour and cocoa into a large bowl, add all the ingredients for the crêpes except butter (sugar, vanilla extract, milk, sparkling water, eggs, salt), mix with a whisk or a mixer (the mixer is better) until the batter is smooth. Add the melted and slightly cooled butter, mix again. The batter will be a bit thinner than the American pancakes batter. It should have the consistency of heavy cream (more or less).
Cover the bowl with a kitchen towel and let stand for about 30-60 minutes (or overnight in the fridge). Stir the dough before cooking the pancakes.
Prepare a non-stick pan (the best is pancake pan, it’s low-rimmed, which makes the flipping very easy, my pan has a diameter of 9-inch/23 cm). Grease it lightly with butter, wipe the butter excess with a paper towel. Heat the pan over high heat (important, the pan must be well-heated!). Grease the pan only before the first crêpe.
Pour the first portion of the batter into the pan, simultaneously tipping the pan so that the mixture spreads evenly (you should hold the pan in your hand at this moment, it should not be on the burner). Pancakes are supposed to be thin, so they need to be cooked very quickly. I cook them over high heat exactly 60 seconds on one side, then 15 seconds on the other (the timing may be different depending on the burner and pan type). Flip the pancakes when they are almost cooked through and their edges are beginning to lift away. Use a spatula to loosen the pancake from all sides, when it moves freely, slide the spatula under the pancake and quickly flip it over. Cook briefly on the other side, transfer to a plate.