In a medium mixing bowl, cream butter and sugar. Add flour a half cup at a time and blend until combined.
Press dough into ungreased tart pan. Bake 25 minutes or until slightly golden. Remove and allow to cool on wire rack.
Filling
Meanwhile, in a large mixing bowl whip heavy cream, on low gradually increasing speed to max until a stiff peak forms.
On medium speed, beat in powdered sugar one tablespoon at a time. Add lemon juice and mascarpone until just blended.
Add mascarpone, blend well.
Add mixture to cooled crust.
Top with seasonal berries or fruits of your choice.
Notes
Substitutions
Butter - Salted or unsalted butter.
Powdered Sugar - If you don't have any on hand you can pulse granulated sugar in a food processor until light and fluffy or substitute granulated sugar.
Lemon Juice - Freshly squeezed or 100% lemon juice.