In a mixing bowl, whisk together flour, sugar, baking powder, salt, and cinnamon.
In another bowl, combine milk, egg, and melted butter until smooth.
Pour wet ingredients into dry ingredients and stir gently until just combined; small lumps are okay.
Fold in diced apples.
Heat a non-stick skillet over medium heat and lightly grease with butter.
Pour about 1/2 cup of batter onto the skillet per pancake. Cook until bubbles form on top (about 2 minutes), then flip and cook for another minute until golden brown.
Serve warm with maple syrup.