1-: Beat together 240 ml whole milk, 120 g sour cream, 4 egg whites, 60 ml fresh lemon juice, zest of 2 lemons, and 5 ml vanilla extract. Set aside.

2-: Sift 270 g all-purpose flour, 200 g granulated sugar, 15 g baking powder, and 3 g kosher salt. Reserve 1 tablespoon flour to coat blueberries.

3-: Cream 170 g unsalted butter until light. Add dry ingredients and mix to a sandy texture.

4-: Gradually add wet ingredients, mixing until just combined.

5-: Toss 190 g fresh blueberries in the reserved flour (and a splash of lemon juice if desired). Fold gently into batter, using a spoon to separate clumps.

6-: Divide batter evenly among pans. Bake 30 minutes or until centers spring back.

7-: Cool in pans 15 minutes, then transfer to wire racks.

8-: Make the Blueberry Reduction Freeze 60 g blueberries for topping. Cook remaining 60 g blueberries with 50 g sugar, 15 ml lemon juice, and 30 ml water over medium-low heat until berries burst and mixture halves. Strain, chill.

9-: Prepare Lemon Buttercream Beat 227 g butter and 2 g salt until fluffy. Gradually add 500 g confectioners’ sugar. Mix in 30-45 ml lemon juice to taste. Blend some with chilled reduction for blueberry buttercream.

10-: Assemble the Cake Pipe a ring of plain lemon buttercream on first layer. Fill ring with blueberry buttercream. Stack layers, crumb coat with lemon buttercream. Frost outside, add dollops and frozen blueberries. Chill before serving.