Preheat oven to 425 degrees Fahrenheit and grease 12 muffin cups.
Sift the dry ingredients - flour, baking powder, and salt - together in a bowl.
In a second bowl, add the butter and beat together with 1/2 cup sugar.
Add the eggs, lemon zest and juice, and the milk. Blend thoroughly.
Add the egg mixture to the dry ingredients and mix until the batter is evenly moist, but no more.
Add the chopped apple.
Drop the batter into the muffin cups.
Stir 1 tablespoon sugar and cinnamon together and sprinkle over the muffins.
Bake about 15 minutes in the oven. A knife inserted into the center should come out clean.
Cool for about 3 to 5 minutes before taking them out of the muffin pan.