Preheat your oven to 350°F (175°C) and prepare a muffin tin with cupcake liners.

In a large mixing bowl, whisk together flour, baking powder, cinnamon, and salt.

In a separate bowl, cream together softened butter and sugar for 3-4 minutes until fluffy.

Add eggs one at a time to the butter-sugar mixture, mixing well after each addition, then stir in vanilla.

Gradually add the dry ingredients to the wet mixture, alternating with milk, and mix until just combined.

In a saucepan, combine the diced apples, lemon juice, brown sugar, and a little butter; cook until apples are tender.

Scoop a tablespoon of batter into each cupcake liner, add some apple filling, then top with more batter.

Bake for 18-20 minutes until golden brown and a toothpick comes out clean.

Allow cupcakes to cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Beat the frosting ingredients together until light and fluffy, then frost cooled cupcakes.

Sprinkle a hint of cinnamon on top for an added festive touch.