In a bowl, whisk together the flour, baking soda, baking powder, and salt.
In another bowl, whisk together the eggs, buttermilk, vanilla, and brown sugar.
Add the flour mixture to the egg mixture and whisk together just until smooth. Then fold in the diced apple.
Cook batter according to your waffle maker instructions. I use ½ batter for my regular waffle iron and 1 cup for my Belgian waffle maker. Makes 8 regular waffles or 4 Belgian waffles.