Separate the eggs.
Split the vanilla pod and scrape out the seeds with a small sharp knife. Put some of the sugar on the cutting board and "mash" the vanilla seeds into the sugar.
Whisk the homemade vanilla sugar together with the egg yolks and salt until light and fluffy.
Add milk and lemon zest.
Sift the flour into the batter and whisk until smooth and uniform.
Beat the egg whites until stiff and gently fold them into the batter (preferably using a spatula). Be careful not to deflate them.
Heat a pan and melt butter on it.
Cook thick pancakes (about 1-1 1/2 centimeters thick) over medium heat. They need a bit more time than thin pancakes to be fully cooked through, so they shouldn't be cooked at too high a heat.
Once the pancakes are cooked, chop them into smaller pieces with a spatula.
Serve warm and sprinkled with powdered sugar.