Prepare the Oven and Cupcake Pan: Preheat the oven to 350°F (175°C). Line a standard muffin pan with paper cupcake liners and set it aside.
Mix the Dry Ingredients: In a medium mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and ground cinnamon until evenly combined.
Cream the Butter and Sugar: In a large mixing bowl, beat the softened butter and granulated sugar until light, fluffy, and creamy. This helps create a soft cupcake texture.
Add the Egg and Vanilla: Add the egg and vanilla extract to the butter mixture. Beat until smooth and fully incorporated.
Combine the Wet and Dry Ingredients: Gradually add the dry ingredients to the wet mixture, alternating with the milk. Mix just until the batter comes together. Avoid overmixing.
Make the Cinnamon Filling: In a small bowl, combine the brown sugar, softened butter, and ground cinnamon. Mix until it forms a thick, smooth cinnamon mixture.
Fill the Cupcake Liners: Spoon some cupcake batter into each lined muffin cup. Add a small amount of cinnamon filling to the center, then cover with more batter. Gently swirl the filling with a toothpick for a cinnamon-roll effect.
Bake the Cupcakes: Bake for about 18 minutes, or until the cupcakes are lightly golden and a toothpick inserted into the cake portion comes out clean or with a few moist crumbs. Transfer the cupcakes to a cooling rack.
Prepare the Cream Cheese Frosting: Beat the softened cream cheese and butter until smooth. Gradually add the powdered sugar and vanilla extract. Add the milk and beat until the frosting is creamy and spreadable.
Frost and Finish: Allow the cupcakes to cool completely before frosting. Spread or pipe the cream cheese frosting over each cupcake. Finish with a light sprinkle of ground cinnamon and serve.