Preheat oven to 350 degreesF. Line 24 standard muffin cups with paper baking cups
Combine flour, baking powder, cinnamon, baking soda, salt and pumpkin pie spice into a medium bowl. Beat sugar and butter in large bowl with electric mixer at medium speed 3 minutes or until light and fluffy. Add egg, one at a time, beating well after each addition.
Combine pumpkin and buttermilk in a small bowl; mix well. Alternately add flour mixture and pumpkin mixture to butter mixture, beating well after each addition. Spoon batter evenly into prepared muffin cups.
Bake 20 minutes or until toothpick inserted into center comes out clean. Cool in pans 10 minutes; remove to wire racks to cool completely.
Prepare vanilla bean buttercream; pipe or spread on cupcakes. Sprinkle with pumpkin sprinkles and orange sugar.
Make vanilla bean buttercream: Beat butter in a large bowl with an electric mixer at medium speed until light and airy. Add vanilla bean paste and beat until well blended. Gradually add powdered sugar, beating until incorporated and mixture is light and fluffy. Add one to two tablespoons milk, if necessary to reach desired spreading consistency.
Notes
If you are piping the buttercream you may want to double the recipe. This makes enough for spreading.