1. Mix the flour and salt, make a well in the center and crack the eggs into it. Add the melted butter, milk, and water. Whisk with a hand or electric whisk. Add the sugar, vanilla sugar, oil, yeast, and optionally rum. Whisk again. The batter should be liquid and smooth. If not, add water.
2. Let it rest for at least 30 minutes. Pour the batter into the greased waffle molds.
3. Cook for about 3 minutes, flipping the waffle iron halfway through cooking.
4. Enjoy these waffles sprinkled with powdered sugar, with jam, Nutella, maple syrup...