Shortbread Crust: Grease with butter, or a non stick cooking spray, a 9 inch (23 cm) pie plate or tart pan with a removable bottom. 

In your food processor, place the flour, sugar, and salt and process to combine. Add the butter and pulse until the pastry starts to come together and form clumps. Place the pastry in the prepared pan and, using your fingertips, evenly press the pastry onto the bottom and up the sides of the pan. (Can use the back of a spoon to smooth the surface of the pastry.) Pierce the bottom of the crust with the tines of a fork. (This will prevent the pastry crust from puffing up while it bakes.) Cover and place the pastry crust in the freezer for 15 minutes to chill. (This will help prevent the crust from shrinking while it bakes.)

Preheat oven to 425 degrees F (220 degrees C) and place rack in center of oven. 

When the pastry is completely chilled, bake until the crust is golden brown, about 13 - 15 minutes. Remove from oven and place on a wire rack to cool while you make the filling.

Filling: Defrost the frozen unsweetened raspberries and then process them in a food processor or blender until pureed. Transfer to a fine mesh strainer placed over a large bowl and force the juice from the berries by gently pressing the berries with the back of a large spoon. (All that should remain in the strainer is the raspberry seeds.)

Then in a small measuring cup sprinkle the gelatin over 1/4 cup (60 ml) of cold water. Let this mixture sit for about five minutes, or until softened, and then microwave for a few seconds to dissolve the gelatin. 

Meanwhile, place the raspberry puree, along with the sugar and jam, in a medium sized saucepan over low heat. Stir with a wire whisk until the jam dissolves and the sauce comes to a boil. Simmer for about 10 minutes, stirring occasionally. Stir in the dissolved gelatin. Remove from heat and stir in the lemon juice. Transfer the raspberry sauce to a bowl and refrigerate until the mixture starts to gel (this will take about 45 to 60 minutes).

Meanwhile, cut the strawberries into 1/4 inch slices. Place the strawberries slices in a large bowl and fold in the thickened raspberry sauce, making sure all the strawberries are coated with the sauce. Pour the strawberries into the baked and cooled pie shell and place in the refrigerator until firm (about three hours).

Serve with softly whipped cream, if desired. Cover and refrigerate any leftovers. Can be stored in the refrigerator for a couple of days.

Serves 8.