1. Melt 1/2 cup unsalted butter in a saucepan over medium-low heat.

2. Remove from heat and stir in lemon juice and lemon zest.

3. Add sugar, cornstarch, and salt. Whisk well.

4. Whisk in egg yolks until smooth, return to heat and cook 10 minutes, whisking constantly until thickened. Do not boil. Set aside and reserve 5 tablespoons for the frosting.

5. Preheat oven to 350°F. Line cupcake pan with paper wrappers.

6. Mix Greek yogurt, milk, vanilla extract, and lemon zest in a bowl. Set aside.

7. In a separate bowl, combine flour, baking powder, and salt. Toss blueberries with 1-2 tablespoons of the flour mixture.

8. Cream butter and sugar until fluffy. Add eggs one at a time, mixing well.

9. Alternately add flour and milk mixtures to the creamed mixture, starting and ending with flour mixture.

10. Gently fold in blueberries and divide batter into cupcake liners, filling each 3/4 full.

11. Bake for 20 minutes or until toothpick comes out clean. Cool in pan for 10 minutes, then transfer to rack to cool completely.

12. To make frosting, beat heavy cream until soft peaks form. Add powdered sugar and vanilla and beat to stiff peaks.

13. Stir 1 tablespoon of whipped cream into reserved lemon curd for filling, and 1 tablespoon into lemon curd for frosting.

14. In another bowl, mix mascarpone with lemon curd (for frosting). Gently fold into whipped cream using a spatula.

15. Use a cupcake corer or knife to remove centers of cupcakes. Fill with lemon curd and replace trimmed tops.

16. Pipe frosting onto cupcakes using a 1M tip or desired piping tip.

17. Garnish with blueberries, yellow sprinkles, and lemon slices.

18. Store cupcakes in the fridge until ready to serve.