Preheat oven to 350

For the Shell:  Place cubed butter, flour, powdered sugar and salt in a food processor.  Blend until the mixture resembles wet sand.  Add the water and mix until the dough comes together to form a ball.  Roll out the dough on a floured surface.  Using a large round cutter, or by hand, cut out circles to fit the selected tart pans.  Gently press dough circles into the bottom and sides of the pans.  Line the tart shells with parchment and fill with pie weights.  Bake for about 15 minutes until shells are set and golden in color.  Allow to cool before removing tart shells from pan.

For the Filling: Place raspberries, rhubarb, sugar, cornstarch and lemon juice in a medium saucepan.  Stir the ingredients so cornstarch and sugar coat the fruit.  Cook over medium high heat, stirring frequently.  Bring the mixture to a bubble and continue cooking and stirring for about two additional minutes while mixture thickens.  Remove from heat and allow to cool.

For the Meringue: Place egg whites, tartar, and salt in a mixing bowl and mix until soft peaks form.  Meanwhile, heat the sugar and water in a small saucepan.  Using a thermometer, cook the sugar mixture to 240 F or 115 C.  With the mixer running, slowly pour the hot sugar syrup into the whipped egg whites.  Continue to beat the meringue mixture until stiff peaks form.

To Assemble:  Spoon raspberry rhubarb compote into the tart shells.  Spoon or pipe meringue over the top of the filling.  Using a kitchen torch or the broiler setting of your oven, toast the meringue.