In a mixing bowl, cream together unsalted butter and granulated sugar until fluffy. Beat in egg, vanilla extract, and strawberry powder. Gradually add in all-purpose flour and salt, stirring until a soft dough forms. Chill the dough in the refrigerator.

Preheat oven to 350°F (175°C). Roll out chilled dough and cut into boat shapes. Transfer to a baking sheet and make indentations in the center of each cookie.

Bake cookies for 12-15 minutes until edges are lightly golden. Let cool on the baking sheet for 5 minutes before transferring to a wire rack.

Whip together mascarpone cheese, heavy cream, and powdered sugar until stiff peaks form. Add vanilla extract and mix briefly. Transfer to a piping bag.

Once cooled, pipe cream filling into each cookie. Top with sliced strawberries and brush warmed strawberry jam over them.

Sprinkle shortbread cookie crumbs around edges if desired. Refrigerate until ready to serve, ideally no longer than 4 hours.