If bacon is not already cooked, do it now. Drain excess grease and chop into small pieces.
In a large bowl, whisk together flour, baking powder, baking soda, and salt.
In another bowl, whisk together milk, eggs, maple syrup, and vanilla. Pour into dry ingredients and whisk until incorporated; a few lumps is fine. Fold in bacon pieces. Let batter rest at least 15 minutes while you prepare the pan.
Preheat your griddle to 350°F or set a frying pan over medium heat. Test heat by flicking water onto the surface; if it sizzles it is ready.
Stir melted butter into batter. Use a ?-cup measure to pour batter onto the griddle. Cook until edges look dry and bubbles form on the top, then flip and cook until golden. Repeat with remaining batter.