Stir the milk, vinegar, and lemon juice together in a bowl; let stand 10 minutes to curdle. Whisk in egg, butter, and vanilla extract.

In a separate bowl, mix together the flour, sugar, baking powder, baking soda, salt, poppy seeds, and lemon zest until well combined. Pour the milk mixture into the flour mixture and whisk a few times until the batter is mostly free of lumps.

Heat a skillet over medium heat and spray with cooking spray. Pour 1/4 cup of batter per pancake into the skillet and cook until bubbles appear on the surface, about 2 minutes. Flip the pancakes over with a spatula and brown the other side, about 2 more minutes.