Preheat oven to 400F.
Dice the butter and return it to the refrigerator while you prepare the flour mixture. Place the flour, salt, and sugar in the bowl of a food processor fitted with a steel blade and pulse a few times to mix. Add the butter and shortening. Pulse 8 to 12 times, until the butter is the size of peas. With the machine running, pour the ice water down the feed tube and pulse the machine until the dough begins to form a ball. Dump out on a floured board and roll into a ball. Wrap in plastic wrap and refrigerate for 30 minutes. Separate dough into 4 balls. Grease tart dishes and press dough with your fingers until even across bottom and sides.
In a large bowl, mix strawberries, rhubarb, sugar, and cornstarch until a thick syrup forms. Stir in lemon zezt, lemon juice, cinnamon and vanilla. Pour equally into crust lined tart dishes.
Mix flour and sugars. Cut butter into mixture until crumbs form. Sprinkle crumbs on top of tarts.Bake for 50 mins or until tart begins to bubble and top starts to brown.