In a small mixing bowl, whisk together the all-purpose flour, baking soda, baking powder, and fine sea salt.
In a separate mixing bowl combine the milk, eggs, sourdough discard, melted butter, sugar, and vanilla extract.
Add the dry ingredients to the wet ingredients and stir just until combined. Avoid overmixing the batter.
Allow the batter to rest at room temperature for 20-25 minutes. In the meantime, preheat the waffle maker. If you abe able to adjust the temperature setting, I set mine to a medium-high setting (setting 4 on my Cuisinart Flip Belgain Waffle Maker, with 5 being the highest/darkest temp setting).
When ready to cook, lightly spray the waffle iron with non-stick cooking spray, then add 3/4 cup of batter to the center of the iron. Gently spread the batter and cook according to your appliance instructions.
Serve immediately with your favorite toppings (we love sliced strawberries and Nutella!) Or, place a cooling rack on top of a baking sheet and add each waffle as you finish cooking them. Place into the oven on a 'keep warm' setting until ready to serve.