Preheat oven to 325 and place rack in center of oven.
Using a hand mixer or bowl mixer, mix butter and sugars in a large bowl until well blended.
Add salt, lemon juice and lemon zest and mix till well incorporated.
Add flour and mix. At first the dough will crumble and fall apart.
Remove dough from bowl and set on a cutting board or counter and gently knead with hands until dough forms a ball.
Take dough in segments and press into tart pans. Start with the bottom and then build up the sides, Dough should be about a 1/4" thick all the way around.
Use a fork to poke holes in the bottom of dough.
Place tins on a cookie sheet.
Sprinkle dough with granulated sugar and bake for 25 minutes or until dough is cooked and slightly golden.
Remove from oven and allow cool completely.
Fill with mascarpone/lemon curd mixture, top with berries, sprinkle with powdered or course granulated sugar, remove tart from tin and serve. Each tart is enough to serve 2 people.