Combine flour, sugar, baking powder, and salt in a bowl.
In a separate bowl, whisk together milk, eggs, melted butter, and vanilla extract.
Mix wet ingredients into dry ingredients until smooth to form the base batter.
Set aside about one-third of the base batter in another bowl.
Add cocoa powder, sugar, red food coloring, and vinegar to the reserved batter and stir well to create the red velvet batter.
Preheat and lightly grease the waffle iron.
Pour some plain batter onto the waffle iron, then spoon the red velvet batter on top.
Swirl lightly using a toothpick or knife to create a marbled effect.
Close waffle iron and cook for 3 to 5 minutes until waffles are crisp and cooked through.
To prepare the optional cream cheese drizzle, mix cream cheese, powdered sugar, milk, and vanilla extract until smooth.
Drizzle the cream cheese glaze over the warm waffles and serve immediately.