From Bon Appetit, http://www.epicurious.com

Makes 6 servings.
Topping
1 cup coarsely chopped walnuts
1/2 cup all purpose flour
1/2 cup (packed) golden brown sugar
1/2 teaspoon ground cinnamon
teaspoon ground ginger
teaspoon salt
Pinch of ground nutmeg
6 tablespoons chilled unsalted butter, cut into 1/2-inch pieces
1 pint vanilla ice cream
cup finely chopped crystallized ginger
Fruit
2 1/2 pounds plums, pitted, quartered
1/2 cup sugar
1 tablespoon cornstarch
1 teaspoon vanilla extract
For topping:
Mix first 7 ingredients in large bowl. Add butter and rub in with fingertips until small moist clumps form. Cover and refrigerate 20 minutes. (Can be made 3 days ahead. Keep refrigerated.)
Microwave ice cream in 5-second intervals just until slightly softened. Mix ice cream and ginger in medium bowl to blend. Cover and freeze. (Can be made 1 day ahead. Keep frozen.)
For fruit:
Preheat oven to 400 F. Toss plums, sugar, cornstarch, and vanilla in bowl. Let stand until sugar dissolves, tossing occasionally, about 5 minutes.
Transfer plum mixture to 11x7-inch glass baking dish. Sprinkle topping over. Bake until topping is dark golden brown and fruit is bubbling, about 40 minutes. Transfer crisp to rack and cool slightly, about 30 minutes.
Scoop warm crisp into shallow bowls. Top each with scoop of ice cream.