Preheat oven to 350°F. Line a 12-cup muffin pan with paper liners.
Mix 1 teaspoon cinnamon with 1/4 cup sugar for topping; set aside.
Whisk flour, baking powder, cream of tartar, 1 1/2 teaspoons cinnamon, and salt.
Beat softened butter with 3/4 cup sugar until pale and fluffy, about 2 minutes.
Stream in beaten eggs and 2 teaspoons vanilla; mix until smooth and creamy.
Add dry ingredients alternately with milk and sour cream; mix just until combined.
Divide batter among liners, about two-thirds full. Sprinkle half the cinnamon sugar on top.
Bake 17–19 minutes until a tester comes out clean. Cool 5 minutes, then cool completely.
For frosting, beat cream cheese and butter until smooth. Add powdered sugar, cinnamon, vanilla, salt, and milk.
Whip until fluffy. Pipe or spread onto cooled cupcakes. Dust with remaining cinnamon sugar.
Notes
Variation: Swap the cream cheese frosting for a simple cinnamon buttercream by using all butter and a splash of cream. For extra snickerdoodle vibes, lightly brush cupcake tops with melted butter before the final cinnamon-sugar dusting.Storage: Refrigerate frosted cupcakes in an airtight container for up to 4 days; bring to room temperature before serving. Unfrosted cupcakes freeze well for 2 months.This recipe is an original creation inspired by classic Easy Snickerdoodle Cupcakes flavors. All ingredient ratios and instructions are independently developed.