In a medium bowl, combine 1 cup of milk with 1 tablespoon of vinegar. Stir gently and let it sit for about 5 minutes to sour the milk.

In a large mixing bowl, whisk together 1 cup of all-purpose flour, 2 tablespoons of sugar, 1 teaspoon of baking powder, 1/2 teaspoon of baking soda, and a pinch of salt.

Once the milk has soured, add 1 egg and 2 tablespoons of melted butter to the bowl. Whisk these ingredients together until smooth.

In a separate bowl, mix 2 tablespoons of melted butter, 1/4 cup of brown sugar, 1 tablespoon of ground cinnamon, and 1 tablespoon of flour until it becomes a smooth paste.

Preheat a nonstick skillet or griddle over medium heat—about 350°F.

Pour 1/4 cup of pancake batter onto the heated skillet for each pancake. Immediately drizzle a spoonful of the cinnamon swirl mixture on top.

Cook the pancakes until bubbles form on the surface and the edges appear set, about 1-2 minutes. Flip them gently using a spatula.

Cook the flipped pancakes for another 30 seconds to 1 minute, or until golden brown and cooked through.

Once all the pancakes are cooked, stack them on a plate and serve warm.