Prepare lemon curd ahead, as directed. Keep chilled until ready to use.
Prepare blueberry puree. In a small saucepan, combine blueberries (fresh or frozen, if frozen do not thaw), lemon zest, lemon juice and sugar. Cook over medium heat, stirring occasionally. When berries are soft, mash with a potato masher. Continue cooking until mixture has thickened. Immediately press through a mesh strainer, into a clean bowl. Allow puree to cool completely prior to using in frosting. If possible, make ahead or chill while cooking the cupcakes.
In a large bowl or stand mixer, cream together butter and sugar until light and fluffy. Mix in eggs, lemon extract, zest and lemon juice. Scrape bowl as needed. Add salt, baking powder and baking soda. Alternate additions of flour and sour cream, mixing until fully combined and no streaks remain.
Divide batter equally between prepared baking cups, using a large cookie scoop or filling roughly 2/3 full. Bake for 16-18 minutes or until a toothpick inserted comes out clean or with a few moist crumbs. Cool in pan until easy to handle, then transfer to a wire rack to cool completely.
When cupcakes have cooled, core and fill cupcakes. Add lemon curd to a small piping bag or sandwich bag, with the tip removed. Using a sharp knife or cupcake corer, carefully remove the center of each cupcake. Do not cut all the way to the bottom. Trim off the bottom portion of the removed cupcake core. Fill each cupcake with lemon curd and replace the top of the cake core back on each cupcake.
In a large bowl or stand mixer, fit with a paddle attachment, beat butter adding 1 cup of powdered sugar at a time. Scrape the bowl as needed. With mixer off, drizzle in 1 tablespoon of puree at a time, increasing speed between additions. Mix until fully combined and no streaks remain. Transfer frosting to a large piping bag fit with desired piping tip. Frost cupcakes as desired, topping off with fresh blueberries prior to serving.
Store cupcakes in an airtight container for up to several days. Cupcakes may also be chilled and brought to room temperature prior to serving.
Nutritional information is provided as a courtesy and is an estimate only. Nutrition information can vary for a variety of reasons. For the most accurate data, use your preferred nutrition calculator with the actual ingredients you used to make this recipe.
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