Make cupcakes: Preheat oven to 375°F. Line 24 mini muffin cups with paper liners. In a bowl, whisk first five ingredients.
In a separate bowl, using an electric mixer at medium-high speed, beat butter and sugar until light, 3 minutes. Whisk egg and pumpkin in a bowl, then beat into butter mixture, scraping down sides of bowl. With mixer on low speed, add flour mixture and yogurt alternately, beginning and ending with flour. Spoon 1 heaping Tbsp. batter into each muffin cup.
Bake until cupcakes spring back when touched lightly, 12 to 15 minutes. Let cool in tin on a wire rack for 5 minutes, then remove from pan and let cool completely on rack.
Make frosting: Beat all ingredients with an electric mixer on medium-high speed until light, 3 minutes. Spread onto cupcakes and serve.