Preheat oven to 375 degrees F (190 degrees C). Spray 2 mini muffin tins with cooking spray.
Mix milk and vinegar together in a bowl; let stand until milk curdles, about 5 minutes. Beat in oil and egg.
Combine flour, sugar, baking powder, baking soda, and salt in a bowl; stir into milk mixture until smooth. Spoon batter into the prepared muffin tins with a tablespoon or a small batter scoop.
Bake in the preheated oven until batter is risen and still pale, about 8 minutes. Remove from muffin cups with a silicone scraper.
