In a large bowl, whisk together the sourdough starter, flour, and milk until smooth.
Let it sit for 10–15 minutes
In a separate small bowl, whisk the egg, melted butter, and vanilla extract.
Stir this mixture into the sourdough batter until well combined.
Add the sugar, baking powder, baking soda, and salt. Mix gently until the ingredients are just incorporated.
Let the batter rest for another 5–10 minutes while you preheat your pan or griddle.
Heat a non-stick skillet or griddle over medium heat and lightly grease it with butter.
Pour about ¼ cup of batter for each pancake.
Cook until bubbles appear on the surface and the edges start to look set, about 2–3 minutes. Flip and cook for another 1–2 minutes on the other side
Stack the pancakes on a plate and serve immediately with your favorite toppings.