1 1/4cupsfrozen raspberries (I think fresh would also work just fine)
2sticks (8 ounces) unsalted butter, VERY soft
3 1/2cupsconfectioners sugar (more if needed), sifted
1tablespoonheavy cream (more if needed)
1/4cupfresh raspberries, for decorating (optional)
For the lemon cupcakes:
Preheat oven to 350 degrees (F). Line a 12 mold muffin tin with paper liners; lightly spray the paper liners with non-stick baking spray; set aside.
In a medium bowl combine flour, baking powder, and salt; mix well to combine; set aside.
In a large measuring cup or bowl combine sour cream, milk, and egg; mix well to combine; set aside.
In a small bowl combine the sugar and lemon zest; rub the lemon zest into the sugar until fragrant and well combined.
In a large bowl or stand mixer fitted with the paddle attachment beat the melted butter and lemon sugar on medium-speed until well combined; about 2 minutes. Add in the lemon juice and beat for another minute on medium-speed. Slowly add the flour mixture to the butter/sugar combination, beating until just combined. Add in sour cream/milk/egg combo and beat on low until *just combined. Over-mixing will result in a dryer/denser cake.
Divide the cupcake batter evenly into the 12 molds, then place the pan in the oven. Bake for 17-19 minutes, or until a toothpick inserted into the center of a cupcake comes out clean (or with just a few solid crumbs). Allow cupcakes to cool in the pan for a few minutes, then transfer them to a cooling wrack to cool completely. Once cool, frost with the raspberry buttercream and extra berries.
For the raspberry buttercream:
Combine the raspberries and lemon juice in a small saucepan; bring to a simmer over medium heat. Once simmering, stir the mixture occasionally, breaking up the berries with a wooden spoon, until the raspberries have become soft enough to mash effortlessly. It will look like raspberry jam. Once the mixture can coat a spoon (you should have about 1/4 cup of raspberry puree) remove from heat. Allow mixture to cool completely before using. <--- That part is SUPER important!
When ready to make buttercream:
Place the softened butter in a large bowl or in the body of a stand mixer. With a handheld mixer, or with the paddle attachment on your stand mixer, beat butter on medium-high (scraping down the sides as needed) until completely smooth; about 2 minutes. Add in the raspberry puree and beat until completely combined; about 1 minute (don't worry if the mixture looks weird at this point). Add in the confectioners sugar, one cup at a time, on low speed. Once all of the sugar has been added, add in the cream and salt, then beat on high-speed for a full 2 minutes - this thickens up the frosting and makes it nice and fluffy. Frost cooled cupcakes as desired.
Store cupcakes in an airtight container, in the fridge, for up to 3 days. Bring to room temperature before serving.