Crust With an electric mixer (or in a food processor), cream together butter and sugar. Add flour and continue to mix until smoothly combined. Add water and mix so that the dough gathers together. Chill in the refrigerator for at least 30 minutes. Roll the dough out thinly and evenly between two sheets of waxed paper, and place in a flan pan or pie plate. Cover the dough with a sheet of foil and weigh this down with dry beans or pastry weights. Bake in a 400°F oven for 10 minutes; remove the foil and weights and bake for another 5 minutes until the pastry is lightly browned. Filling In a double boiler, melt the white chocolate and butter. Add cream, mix well, remove from heat and allow it to cool down a little. Arrange the raspberries on the bottom of the pastry shell, and carefully spoon the white chocolate over them to cover. Sprinkle with chopped pistachio nuts and refrigerate for at least 2 hours before serving in flan wedges. (or freeze and cut into bite sized squares if you're preparing an assortment of squares and desserts for a larger gathering).