Combine milk with vinegar in a medium bowl and set aside for 5 minutes to "sour." Combine flour, sugar, baking powder, and salt in a large mixing bowl. Whisk egg and butter into soured milk. Pour the flour mixture into th ewet ingredients and whisk until large lumps are gone. Heat a large skillet over medium heat and coat with cooking spray. Pour 1/4 cupfuls of batter onto the skillet and cook until bubbles appear on the surface. Flip with a spatula and cook until browned on the other side.