First, whisk together the flour, sugar, baking powder, baking soda, and salt in a large bowl.
In a separate bowl, whisk together the sourdough discard, egg, milk, melted butter, and vanilla extract until smooth.
Next, pour the wet ingredients into the dry ingredients and stir gently until just combined. Do not overmix. A few lumps are completely fine and help keep the pancakes tender.
Allow the batter to rest for about 5–10 minutes before cooking. During this time, the sourdough starter and baking soda begin reacting, helping create extra fluffy pancakes.
Heat a lightly greased skillet or griddle over medium heat. Scoop about ¼ cup batter for each pancake. Cook until bubbles form on the surface and the edges begin setting. Then flip and cook the second side until golden brown.