1. Press butter pastry evenly over bottom of an 11-inch plain or fluted tart pan with removable rim; then press pastry up pan sides.
2. Bake in a 300° oven until pale gold, 12 to 15 minutes. Use hot or cool.
3. Meanwhile, in a bowl, beat to blend eggs, sugar, crystallized ginger, fresh ginger, and vanilla.
4. Rub macadamia nuts in a towel to remove excess salt. Lift nuts from towel and put in bowl. Mix and pour into pastry.
5. Bake on lowest rack in a 350° oven until top is golden and filling is set (test by gently shaking), 35 to 40 minutes. Cool tart on a rack. Remove pan rim and cut tart into wedges. Spoon warm chocolate sauce onto portions and accompany with ice cream.
Butter pastry: In a food processor or a bowl, combine 1 1/3 cups all-purpose flour and 1/4 cup sugar. Add 1/2 cup (1/4 lb.) butter or margarine, in chunks, and whirl or rub with your fingers until fine crumbs form. Add 1 large egg yolk; whirl or mix with a fork until dough holds together.
Warm chocolate sauce: In a microwave-safe bowl or a 1- to 1 1/2-quart pan, melt 1 1/2 cups semisweet chocolate chips with 3/4 cup half-and-half (light cream) or milk in a microwave oven or over low heat, stirring often until sauce is smooth. Serve warm. Makes about 2 cups.