Preheat your oven to 350°F (175°C).

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

In a separate bowl, cream together the softened butter and granulated sugar until light and fluffy.

Beat in the eggs, milk, and vanilla extract until just combined.

Gradually add the dry ingredients to the butter mixture, mixing until just combined.

In another bowl, mix the brown sugar and ground cinnamon.

Pour half of your muffin batter into a greased or lined muffin tin, then sprinkle half the cinnamon filling over the batter.

Add the remaining batter followed by the last of the cinnamon filling.

Use a knife or skewer to gently swirl the filling through the batter.

Bake for about 20-25 minutes or until a toothpick comes out clean when inserted.

Allow your muffins to cool in the pan for 5 minutes before transferring them to a wire rack.

If desired, mix powdered sugar with milk to create a quick glaze and drizzle over cooled muffins.