Yellow Cupcakes With Chocolate Ganache Frosting

1. FOR THE CUPCAKES: Adjust oven rack to middle position and heat oven to 350 degrees. Line 12-cup muffin tin with paper or foil liners.
2. Whisk flour, sugar, baking powder, and salt together in bowl of stand mixer. Fit stand mixer with paddle and beat flour mixture, butter, sour cream, egg, egg yolks, and vanilla together on medium speed until smooth and satiny, about 30 seconds. Scrape down bowl, then mix by hand using rubber spatula until smooth and no flour pockets remain.
3. Using ice cream scoop or large spoon, divide batter evenly among prepared muffin cups. Bake cupcakes until tops are pale gold and toothpick inserted in centers comes out clean, 20 to 24 minutes. Lift each cupcake from tin and transfer to wire rack. Let cupcakes cool completely, about 45 minutes, before frosting.
4. FOR THE FROSTING: Place chocolate in medium heatproof bowl. Bring cream to boil in small saucepan. Pour boiling cream over chocolate, and let sit, covered, for 5 minutes. Whisk mixture until smooth, then cover with plastic wrap and refrigerate until cool and slightly firm, 45 minutes to 1 hour.
5. Using stand mixer fitted with whisk, whip cooled chocolate mixture on medium speed until fluffy and mousselike and soft peaks form, about 2 minutes.
6. Spread 2 to 3 generous tablespoons frosting over each cooled cupcake and serve.

These cupcakes are best eaten the day they are made, but unfrosted extras will keep in an airtight container at room temperature for up to 3 days. To double the recipe, use 3 whole eggs and 2 yolks, and double the remaining ingredients.