In a saucepan, combine fresh blueberries with lemon juice over medium heat, stirring until berries soften, about 5 minutes.

Strain the mixture to extract the juice.

In a mixing bowl, beat room temperature butter and sugar until light and fluffy.

Gradually add egg yolks and blueberry juice, then cook over low heat until thickened, reaching 170°F.

Chill the curd in the fridge.

Preheat oven to 350°F and line a 12-cup muffin tin with liners.

Beat unsalted butter, vegetable oil, and sugar until fluffy, about 4 minutes.

Add eggs one at a time, mixing well after each addition, then stir in vanilla.

Mix dry ingredients and wet ingredients alternately with milk until smooth.

Dust blueberries with flour to prevent sinking.

Gently fold flour-coated blueberries into the batter.

Spoon batter into lined cupcake wells, filling each about two-thirds full.

Add a few extra blueberries on top.

Bake filled cupcake tin for approximately 18 minutes, or until toothpick comes out clean.

Cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.

Set up a double boiler and whisk egg whites and sugar until 140°F.

Remove from heat and whip until stiff peaks form, about 7 minutes.

Gradually add room temperature butter, mixing until smooth.

Incorporate chilled blueberry curd.

Create a hole in the center of each cooled cupcake.

Spoon blueberry curd into each hole, filling generously.

Pipe blueberry Swiss meringue buttercream on top.