Combine whole milk and buttermilk, and warm to 80°F/26.6°C
Sift flour, yeast, salt, sugar, and cornstarch in a large bowl, making a well in the center; Stir in milk mixture with a whisk until smooth; Stir in beaten eggs; Stir in melted butter and incorporate fully; Stir in vanilla extract.
Use plastic wrap to cover the bowl, and rest at room temperature for 1 hour; the mixture will begin to bubble. You can also proof in a warm oven (90°F/32°C), and it will reduce resting time to 30 minutes. You may also make this the night before and refrigerate overnight for a deeper flavor. Allow the batter to come to room temperature before baking in the waffle iron.
Season and preheat your waffle iron as per the manufacturer's instructions. Pour batter onto the iron as per manufacturer's instructions (approximately 200ml). Close the lid and bake for the recommended amount of time, or until the waffle is golden brown (time varies with the waffle iron; approximately 6 minutes, longer if a extra-crispy exterior is desired).
Serve immediately, or keep warm in a 200°F/93°C oven.
