In a medium saucepan over medium heat, combine fresh blueberries and lemon juice, cooking until soft, about 5 minutes. Strain and return juice to saucepan. Whisk in sugar and butter, followed by egg yolks, stirring constantly over low heat until thick, reaching 170°F. Refrigerate for at least 2 hours.

Preheat your oven to 350°F and line cupcake tin with liners. Cream together unsalted butter and vegetable oil with sugar until light and fluffy, about 3 minutes. Gradually add in eggs and vanilla extract, then alternate adding flour mixture and milk, blending until smooth.

Toss blueberries in a tablespoon of flour to help them stay suspended. Scoop cupcake batter into lined cups, filling about one-third full. Add floured blueberries, then cover with another layer of batter, filling about two-thirds full.

Bake in preheated oven for 18 minutes, until tops spring back when touched and a toothpick comes out clean. Cool in tin for 5 minutes before transferring to wire rack to cool completely.

For Swiss Meringue Buttercream, create a double boiler and whisk egg whites and sugar to form warm syrup (about 140°F). Remove from heat and whip until stiff peaks form. Gradually add softened butter and fold in blueberry curd.

Once cupcakes are cooled, use a knife or corer to remove a portion from each center. Fill each cavity with blueberry curd and pipe buttercream on top, decorating with fresh blueberries.