In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt. Set aside.
In another bowl, whisk together buttermilk, eggs, and vanilla.
Make a well in the center of the dry ingredients and pour in the buttermilk mixture. Stir until just blended; a few lumps is OK. Stir in the chocolate chips. Let batter rest while you preheat your waffle maker.
Once the waffle iron is ready, stir the melted butter into the batter. Pour batter onto waffle iron and cook according to your waffle iron's instructions. Repeat with remaining batter.
Notes
If batter is too thick, stir in an additional ¼ cup buttermilk.