1. Make the Pastry: Stir the salt into the ice water until dissolved. In a food processor, combine the 3 1/2 cups of flour and the butter and pulse until the butter is the size of peas and evenly distributed in the flour. Make indentations in the flour mixture and drizzle in the water. Pulse just until the flour is moistened. Scrape the mixture out onto a lightly floured work surface and quickly press and squeeze just until a shaggy, coarse dough forms. Flatten the dough into a disk, wrap in plastic and refrigerate for 30 minutes.
2. On a floured work surface, dust the top of the pastry with flour. Roll out to an 8-by-15-inch rectangle. Fold the rectangle into thirds like a letter, brushing off any excess flour. Roll it out to a rectangle and fold it again, dusting with more flour as necessary. Cover and refrigerate for 30 minutes. Roll and fold 2 more times, refrigerating the pastry for 30 minutes in between. Refrigerate the pastry for 1 hour.
3. Preheat the oven to 425°. Cut out a 10-inch round of parchment paper. Line a large rimmed baking sheet with parchment. Divide the pastry in half; freeze half for another use. On a floured work surface, roll out the pastry 1/4 inch thick. Using a sharp knife and a 12-inch plate as a template, cut out a 12-inch round. Brush off any excess flour and transfer the pastry to the prepared baking sheet. Top with the parchment round and a 10-inch cake pan; fill the pan with pie weights or dried beans.
4. Bake the pastry in the middle of the oven for 10 minutes. Reduce the oven temperature to 375° and bake for about 35 minutes, until starting to brown around the edge. Remove the cake pan and parchment round and cover the edge of the pastry with foil. Bake the pastry in the upper third of the oven for about 15 minutes longer, until the center of the round is lightly browned and crisp. Transfer the pastry to a rack to cool.
5. Assemble the Tart: In a large bowl, whip the cream to soft peaks. Add the granulated sugar and Grand Marnier and whip the cream until firm. Spread the whipped cream over the pastry and arrange the sliced strawberries on top. Dust the tart with confectioners' sugar, cut into wedges and serve.