Lemon Cupcakes w/ Lemon Curd Filling and Lemon Icing

I made these last night for a tennis match and they were a hit.  Someone even asked me if I bake for a living :) 

Lemon curd is not difficult to make.  There are many recipes online.  To make things simple last night I just used jarred lemon curd from the grocery store.  I put it into a pastry bag and used that to pipe it into the cupcakes.

Makes 2 1/2 dozen cupcakes

FOR THE CUPCAKES
3 1/2 cups (445 grams) all-purpose flour
1 teaspoon baking soda
1/2 teaspoon baking powder
1/2 teaspoon salt
1 cup (2 sticks or 226 grams) unsalted butter, softened
2 cups (400 grams) sugar
3 eggs
2 teaspoons finely grated lemon zest
1 teaspoon (5 ml) vanilla
1 - 1 lb. package (about 2 cups) sour cream
Preheat the oven to 350 degrees (180 C). Line a muffin pan with cupcake liners.
In a medium bowl, combine the flour, baking soda, baking powder, and salt; set aside.
In a large bowl, or the bowl of a standing mixer, cream the butter and sugar together until light and fluffy. Add the eggs one at a time, scraping the bowl between additions. Stir in the zest and vanilla until thoroughly combined. Add one-third of the flour mixture and mix until just combined. Stir in half of the sour cream until just mixed in. Repeat this process with the remaining flour and sour cream until all of the ingredients are combined. Scrape the bowl, then stir the batter for another 20 to 30 seconds to make sure everything is mixed in.
Fill the prepared muffin pans with 3 tablespoons of batter in each cup. Bake for 20 to 25 minutes, or until the tops are just turning golden brown. Transfer to a wire cooling rack and allow to cool completely before frosting.


FOR THE FROSTING
1/2 cup (1 stick or 113 grams) unsalted butter, at room temperature
6 cups confectioners' sugar
1/4 cup (2 ounces) lemon juice
1/2 teaspoon vanilla
1/2 teaspoon finely grated lemon zest
2 tablespoons (30 to 45 ml) heavy cream (start with 1 tablespoon, adding more, as needed)
In a large bowl, or the bowl of a standing mixer, beat the butter for 3 minutes. Beat in half of the sugar, and all of the lemon juice and the zest, until combined. Add the remaining sugar, the vanilla, and the cream (as needed), and whisk on high for 4 minutes, until light and fluffy. If the frosting is too thick, add more cream, 1/2 teaspoon at a time, until desired consistency is reached.

TO ASSEMBLE
Core a small amount out of the center of each cupcake and pipe in lemon curd filling.  Replace the top of the core and then top with the frosting.