3cups (6 sticks or 680 g)butter, at cool room temperature
6cups (681 g)powdered sugar, sifted
1cup (about 12 g)freeze-dried strawberries
2½cups (375 g)fresh or frozen blueberries(no need to thaw frozen berries)
4½tbsp (56 g)granulated sugar
2tspcornstarch (or arrowroot)
about ½cupfresh blueberries
FOR THE CUPCAKES
Preheat oven to 350°. Line 2 12-cup muffin pans with cupcake liners.
In bowl of stand mixer (or hand held mixer), combine sugar, oil, and eggs and mix on medium speed until well combined and thickened slightly. Add sour cream and vanilla extract and mix just until combined. Scrape down sides and bottom of bowl.
Whisk together flour, baking powder, and salt in large bowl.
Add half the dry ingredients until almost combined, then add half the milk. Repeat this with other half of dry followed by other half of wet. Don't overmix.
Fill cupcake liners about ¾ full about 20-25 minutes, or until top springs back when lightly touched, or a toothpick inserted into the center comes out almost clean.
Cool the cupcakes in the pan for about 10 minutes and then transfer to a wire rack to cool completely before filling and frosting.
FOR THE BLUEBERRY COMPOTE
In medium saucepan, combine blueberries, sugar, lemon zest, and butter over medium heat, stirring constantly at first so sugar doesn't burn. Crush the berries while stirring to release juices.
Cook for about 5 minutes until blueberries begin to break down and sugar has dissolved.
Combine lemon juice with cornstarch in small bowl and add to blueberry mixture. Stir for a few minutes until mixture thickens considerably.
Remove from heat and pour into a bowl. Cover and refrigerate until mixture is completely cooled before using.
FOR THE BUTTERCREAM
Cream butter in bowl of stand mixer fitted with paddle attachment. This should only take about 30 seconds to a minute, depending on the temperature of the butter.
Scrape down the sides of the bowl and slowly add the powdered sugar in about 1-2 cup increments, pulsing on low until combined. When all the sugar has been added, scrape down the sides and bottom of the bowl again.
Add the vanilla extract. Then increase the speed to high and whip the buttercream until smooth, creamy, and lighter in color, about 5 minutes. Stop the mixer once or twice to scrape the bowl and paddle.
Use right away, or store in an airtight container in the refrigerate for about one week, or freeze for up to three months. When ready to use, bring to room temperature before re-whipping it briefly.
FOR THE STRAWBERRY BUTTERCREAM
In bowl of a food processor or small blender (I used my Ninja smoothie cup), pulverize freeze-dried strawberries to a fine powder.
Add powder to about ⅓ of vanilla buttercream, along with strawberry preserves, and combine well.
DECORATING THE CUPCAKES
To fill pastry bag for swirls, divide buttercream into three parts. Make the strawberry buttercream as above and add it to one smaller pastry bag, cutting off about 1/2-1 inch of the point and sealing the bag with a rubber band. With another third, add blue food coloring (I prefer paste colors) and stir to combine well. Fill this in another smaller pastry bag just like the strawberry. Fill the third pastry bag with the plain vanilla (white) buttercream. Don't overfill any of the bags or they won't fit in the larger bag.
Place each bag side by side into a larger decorating bag fitted with a 1M star tip. Twist bag to seal and slowly squeeze bag to perform a test swirl on a plate or piece of parchment. Once all three colors are coming out, proceed to decorate cupcakes with the swirled frosting.