1. Prepare the Batter the Night Before: In a large mixing bowl, combine the sourdough discard, all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Whisk these dry ingredients together thoroughly to ensure everything is evenly distributed.

2. Add Wet Ingredients: In a separate medium bowl, whisk together the milk, melted butter, eggs, and vanilla extract until well combined.

3. Combine Wet and Dry: Pour the wet ingredient mixture into the dry ingredient mixture. Stir gently with a whisk or spatula until just combined. Be careful not to overmix; a few lumps are perfectly fine and will result in a more tender waffle.

4. Overnight Rest: Cover the bowl tightly with plastic wrap and place it in the refrigerator. Let the batter rest overnight for at least 8 hours, or up to 12 hours. This resting period allows the sourdough to work its magic and the flavors to meld.

5. Preheat Waffle Iron: The next morning, remove the batter from the refrigerator. It might be slightly thicker than when you first mixed it. Preheat your waffle iron according to the manufacturer’s instructions. Lightly grease the plates with cooking spray or a brush of melted butter, even if it’s non-stick.

6. Cook the Waffles: Pour or scoop the desired amount of batter onto the hot waffle iron (the amount will vary based on your waffle iron size). Close the lid and cook for 3-5 minutes, or until the waffle is golden brown and crisp, and steam is no longer escaping from the sides.

7. Serve Immediately: Carefully remove the cooked waffle from the iron and serve hot with your favorite toppings. Repeat with the remaining batter.