• Preheat the oven to 350°F (175°C) and line a 12-cup muffin pan with cupcake liners.
• Combine the granulated sugar and ground cinnamon for the swirl in a small bowl and set aside.
• Whisk the flour, baking powder, and salt together in a medium bowl.
• In a large bowl, combine the melted butter and granulated sugar until well mixed.
• Add the eggs one at a time, mixing after each addition.
• Mix in the vanilla extract, sourdough discard, sour cream, and whole milk until combined.
• Gradually add the dry ingredients to the wet ingredients and mix just until the flour disappears. Do not overmix.
• Spoon a small amount of batter into each cupcake liner.
• Sprinkle some of the cinnamon-sugar mixture over the batter.
• Add another layer of batter and sprinkle the remaining cinnamon-sugar mixture over the tops.
• Gently swirl the batter with a toothpick to distribute the cinnamon sugar.
• Fill each liner about two-thirds full.
• Bake for 18-22 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
• Let the cupcakes cool in the pan for 5 minutes, then transfer them to a wire rack.

How To Cinnamon Cream Cheese Frosting

• Beat the softened cream cheese and butter together until smooth and creamy.
• Gradually add the sifted powdered sugar, mixing until smooth.
• Add the cinnamon and vanilla extract and beat until the frosting is fluffy and easy to pipe.
• Transfer the frosting to a piping bag fitted with a star tip.
• Pipe the cinnamon cream cheese frosting onto the completely cooled cupcakes.
• Sprinkle a little cinnamon sugar over the frosting before serving.