In a medium bowl, whisk together the flour, sugar, baking powder and salt. In a small bowl, whisk together the milk, eggs, oil or butter and vanilla. Add to the dry ingredients and whisk just until blended. Stir in the pecans, if you're using them.
Preheat your waffle iron and spray it with nonstick spray or brush it with oil. Ladle in some batter - about 1/2 cup, or however much you usually cook at a time, close the lid and cook according to the manufacturer's directions, or until golden and crisp. Serve immediately, or keep warm on a rack set on a baking sheet in a 250F oven while you cook the rest.