Prepare the filling: eggs, two types of flour and mild mustard lightly whisk with a small amount of milk, as soon as the mixture is evenly mixed, add the remaining milk, salt to taste (mustard is already salty, do not forget about it). Once again, mix everything evenly and pour the liquid mixture into the mold on the onion. Now the form is filled almost to the brim. We level the surface (in the photo, the surface without leveling) and put it in a preheated 180 ° oven for 1 hour. After 30-40 minutes, you look to see if this is the tip. Personally, at this moment I lower the temperature to 170 ° and bake the remaining time with it.