Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners. Set aside.

In a large bowl, whisk together flour, baking powder, baking soda, and salt until thoroughly combined.

In a separate medium bowl, combine the melted butter and 1 cup of granulated sugar, stirring until well blended. Allow this mixture to cool slightly at room temperature.

Once cooled, whisk in the egg, sour cream, milk, and vanilla extract until the wet ingredients are smooth and cohesive.

Gradually fold the dry mixture into the wet ingredients, stirring gently until just combined—take care not to overmix to keep the batter light.

In a small bowl, mix the remaining 1/4 cup of sugar with the cinnamon, creating a cinnamon-sugar topping.

Spoon about 2 tablespoons of batter into each prepared cupcake liner, then sprinkle with 1 teaspoon of the cinnamon-sugar mixture.

Top each with additional batter until the liners are approximately 3/4 full, finishing with another sprinkle of cinnamon sugar on top.

Bake in the preheated oven for 16-20 minutes or until a toothpick inserted into the center of a cupcake comes out clean.

Allow the cupcakes to cool completely on a wire rack before frosting.

In a mixing bowl, beat together the softened cream cheese and butter using a stand or hand mixer until the mixture is fluffy and smooth.

Gradually add the powdered sugar, one cup at a time, beating until well incorporated.

Stir in the vanilla extract and cinnamon, mixing until the frosting becomes light and airy.

Transfer the frosting to a piping bag fitted with a star tip and pipe swirls onto the cooled cupcakes.

Serve these delicious snickerdoodle cupcakes and enjoy!