Combine the flour, sugar, baking powder, baking soda, and salt in a large bowl. Cut in the butter using a pastry blender or large fork.
Whisk buttermilk, eggs, vanilla, and milk in a separate bowl. Add to the dry ingredients and whisk until barely combined. It's fine if there are a few lumps. Batter will be quite thick.
Heat your waffle iron and brush it with vegetable oil (or use cooking spray.) Spoon about a cup of waffle batter into the hot waffle iron. Cook until golden brown.
Serve hot with butter and maple syrup, or whipped cream and fresh berries.
Notes
I sometimes substitute about 1/2-3/4 cup of the flour with whole wheat flour and no one can tell the difference. :)
To keep waffles warm before serving. heat your oven to 200 or 250 degrees. Place waffles in a single layer on a cookie sheet. Use a cooling rack to stack additional layers as needed. Air will circulate and the waffles won't get soggy.