Preheat the oven to 350 degrees F and line a cupcake pan with paper liners.
In a large bowl, add the 1 ¼ cups all purpose flour, 1 cup granulated sugar,1 cup granulated sugar1/4 cup unsweetened cocoa powder, 1 teaspoon baking powder, 1/4 teaspoon salt, and ½ teaspoon ground cinnamon. Whisk until combined.
In a separate bowl, add the ½ cup whole milk, ⅓ cup canned pumpkin puree, ¼ cup vegetable oil, 2 large eggs, and 1 teaspoon vanilla extract. Whisk until incorporated.
Add the wet ingredients to the dry and whisk just until combined. Scrape down the edges and bottom of the bowl.
Fill each cupcake liner ¾ of the way full.
Place in the preheated oven and bake for 15-18 minutes or until a toothpick inserted into the center of a cupcake comes out clean.
Allow the cupcakes to cool 5 to 10 minutes in the pan before transferring them to a wire rack and cool completely.
Chocolate Buttercream
Add the 1/2 cup butter to a large bowl or stand mixer bowl. Beat on medium speed until light and fluffy, about 2 to 3 minutes with the hand mixer or 1 minute with stand mixer.
With the mixer on low, slowly add the 2 cups powdered sugar.
Once all of the powdered sugar has been incorporated, add the melted 6 ounces milk or semi-sweet baking chocolate and 1 teaspoon vanilla extract. Beat just until combined. Scrape down the sides and bottom of the bowl.
Turn the mixer to medium high speed and beat until the frosting comes light and fluffy, about 1 minute.
Add the frosting to a piping bag fitted with a Wilton 1M tip.
Pipe tall swirls of frosting on each cupcake.
Place the cupcakes in an airtight container at room temperature.
Notes
Storage: Store in an airtight container at room temperature for up to 4 days.