Reserve 3 or 4 whole nuts for garnish. Rub remaining macadamias in a towel to remove excess salt; lift nuts from towel and set aside.
With your fingers or a food processor, mix or whirl flour, 1/2 cup sugar, and butter until mixture is fine crumbs. Add egg and mix with a fork or whirl until dough holds together; pat into a ball.
Press 2/3 of the pastry over the bottom and sides of a 1 1/2-inch-deep, 9-inch-wide round cake pan with removable rim. Cover and chill. Roll remaining pastry between 2 sheets of waxed paper into a 9-inch-wide round. Chill flat.
Meanwhile, pour remaining 2 cups sugar into a 10- to 12-inch nonstick frying pan. Set over medium-high heat and stir often until sugar melts and turns pale amber, about 7 minutes.
Pour in cream (mixture will bubble up) and remove from heat. Stir until sauce is smooth, about 5 minutes. Stir in nuts (except those reserved for garnish). Let nut mixture cool 10 to 20 minutes, then pour into pastry shell.
Peel 1 sheet of waxed paper from pastry round and invert pastry onto nut-filled torte. Peel off remaining paper. Fold edges of top pastry in until flush with pan rim. Press pastry rim with the flour-dipped tines of a fork to seal. Brush top of torte lightly with beaten egg white.
Bake in a 325° oven until deep golden brown, about 1 hour.
Cool in pan on a rack 10 to 20 minutes. Run a thin knife between pastry and pan rim. Remove rim and let torte cool.
Garnish with reserved macadamia nuts. Cut into thin wedges.