In a large mixing bowl, whisk together flour, baking powder, salt, and sugar until evenly combined. In a separate bowl, mix milk, egg, and melted butter until smooth.
Pour the wet ingredients into the dry ingredients and stir gently until just combined; some lumps are okay. Do not overmix to keep the batter fluffy.
Combine brown sugar, cinnamon, and a few teaspoons of flour in a small bowl to make the cinnamon swirl mixture. Mix until crumbly.
Pour about 1/4 of the pancake batter onto a preheated, greased griddle or non-stick skillet over medium heat. Use a spoon or squeeze bottle to gently spread a teaspoon of cinnamon mixture onto the wet batter, creating swirls as you layer.
Cook the pancake until bubbles form on the surface and the edges are set, about 2-3 minutes. Flip carefully with a spatula and cook for another 2 minutes, until golden brown and cooked through. Repeat with remaining batter, adding more cinnamon swirl as desired.
Serve the pancakes hot, stacked on a plate. Optionally, top with additional cinnamon sugar, butter, or syrup for extra flavor.
