In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Set aside.

In a separate medium bowl, whisk together the buttermilk, large eggs, and melted and cooled unsalted butter until well combined.

Pour the wet ingredients into the dry ingredients. Whisk until just combined. Be careful not to overmix; a few lumps are okay. Divide this batter evenly into two separate large bowls.

To the first half of the batter, add 1/2 tsp of the divided vanilla extract. Stir gently until fully incorporated. This is your vanilla batter.

To the second half of the batter, add the unsweetened cocoa powder, red food coloring, and the remaining 1/2 tsp of vanilla extract. Whisk thoroughly until the color is uniform and the cocoa is fully incorporated. This is your red velvet batter.

Preheat your waffle iron according to the manufacturer's instructions. Lightly grease the waffle grids if necessary.

For each waffle, drop alternating dollops (about 2-3 tablespoons each) of vanilla batter and red velvet batter onto the hot waffle iron. Try to distribute them somewhat evenly.

Using a skewer or a knife, gently swirl the batters together 1-2 times to create a marbled effect. Be careful not to overmix, as you want distinct swirls.

Close the waffle iron and cook for 3-5 minutes, or until the waffle is golden brown, crisp, and steam is no longer escaping. Cooking time may vary based on your waffle iron model.

Carefully remove the cooked waffle and place it on a wire rack to prevent it from getting soggy while you cook the remaining waffles.

Serve the Red Velvet Marble Waffles immediately with your favorite optional toppings such as cream cheese glaze, whipped cream, fresh berries, or a dusting of powdered sugar.