In a large mixing bowl, combine the sourdough starter, flour, sugar, baking powder, baking soda, and salt. Whisk together until well mixed.
In a separate bowl, whisk together the milk, egg, melted butter, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and gently stir until just combined. Be careful not to overmix; a few lumps are okay.
Heat a non-stick skillet or griddle over medium heat and add a small amount of butter to coat the surface.
Pour about 1/4 cup of batter onto the skillet for each pancake. Cook until bubbles form on the surface and the edges look set, about 2-3 minutes. Flip and cook for an additional 1-2 minutes until golden brown.
Repeat with the remaining batter, adding more butter to the skillet as needed.