For tart shells: In a large bowl using a pastry cutter or two forks - mix butter, flour and salt until dough becomes crumbly. Add water 2 tablespoons at a time until consistency is smooth. Wrap dough in plastic wrap and chill for 30 minutes.
While the dough is chilling, Combine all filling ingredients in a non-stick saucepan. Cook over medium-low heat, stirring constantly until butter is melted and mixture thickens slightly, Do not allow filling to boil. Remove from heat, transfer to a bowl and cool.
Preheat over to 400 degrees F. Roll out dough on cutting board and cut 3" circles using a scalloped cookie/doughnut cutter. Place into greased cupcake pan, pressing sides of dough to fit.
Pour filling into dough cups and bake 15 to 18 minutes, Let cool,
In a stand mixer, whip the cream, sugar and vanilla until stiff. Top the tarts with whipped topping and garnish with fresh blueberries.
Recipe by Purely Katie at https://www.purelykatie.com/mini-lemon-tarts/