Place the frozen unsweetened raspberries and the sugar in a small saucepan and bring to a boil over medium heat.

Reduce the heat and simmer, stirring occasionally, for about 15 to 20 minutes or until most of the liquid has evaporated. Do not let it burn.

Remove from heat and pour into a heatproof measuring cup. You should have about 1 cup of preserves.

Stir in the 1 tablespoon raspberry preserves and add a drop or two of lemon juice. Cover and place in the refrigerator while you make the crust. (This jam can be made several days ahead and stored in the refrigerator.)

For the Pate Brisee, In a food processor, place the flour, salt, and sugar and process until combined.

Add the butter and process until the mixture resembles coarse meal (about 15 seconds). Pour 1/8 cup (30 ml) water in a slow, steady stream through the feed tube until the pastry just holds together when pinched. Add remaining water, if necessary. Do not process more than about 30 seconds.

Turn the pastry out onto your work surface, gather it into a ball, cover with plastic wrap, and refrigerate for about one hour to chill the butter and allow the gluten in the flour to relax.

Once the pastry has chilled, remove from refrigerator and place on a lightly floured surface. Roll the pastry into an 11 inch (28 cm) round.

To prevent the pastry from sticking to the counter and to ensure uniform thickness, keep lifting up and turning the pastry a quarter turn as you roll (always roll from the center of the pastry outwards to get uniform thickness).

Transfer the pastry to a parchment paper lined baking sheet. Spread the raspberry jam over the pastry, leaving about a 2 inch (5 cm) border.

Gently fold the edges of the pastry up and over the filling, pleating as necessary, to form an 8 inch (20 cm) round. Make sure to seal any cracks in the pastry.

Bake the tart in a preheated 400 degree F (205 degree C) oven for about 30 minutes or until the pastry is golden brown. Remove from oven and place on a wire rack to cool.

Sprinkle with chopped walnuts or almonds and dust the top of the crostata with powdered sugar. Serve plain or with softly whipped cream.