Prepare the buttermilk: Mix 370ml milk with 15g vinegar and let it rest for 10 minutes to curdle, or substitute with 385ml buttermilk.
Mix dry ingredients: In a bowl, combine the flour, brown sugar, baking soda, baking powder, and salt.
Combine wet ingredients: In another bowl, beat the egg, then add the prepared buttermilk (or buttermilk substitute), melted butter (not hot), and vanilla extract.
Make the batter: Pour the wet ingredients into the dry ingredients and gently mix until just combined. Do not overmix.
Cook the pancakes: Heat a non-stick pan or griddle over medium heat. Pour batter to form pancakes of desired size. Cook until bubbles form on the surface and edges look set, then flip and cook until golden on the other side.
Serve: Serve warm with your favorite toppings.