Place flour, sugar, baking soda, and salt in mixing bowl and stir to combine.
In a second bowl, whisk eggs, buttermilk, and vanilla until blended. Stir wet mixture into dry ingredients. Stir in lemon juice and zest. Fold in melted butter and then vanilla yogurt with a rubber spatula or wooden spoon. Let batter rest a few minutes before using.
Pour batter onto the center of the lower grid. Allow batter to spread toward edges for 5 seconds. Close lid of waffle iron and cook according the waffler instructions. Repeat with remaining batter.
For best results, serve immediately.
For lemon ginger waffles, add 1 tablespoon of grated fresh ginger to the batter with the juice and zest. For lemon blueberry waffles add 1 cup of blueberries to the batter as the last ingredient.