According to the crumb recipe on the Epicurious Website, the crumb mixture should be the texture of wet sand and then packed sowndown on the mound of filling:
1 cup all purpose flour
1/2 cup sugar
1/4 cup (packed) golden brown sugar
1 1/2 teaspoons ground cinnamon
1/2 teaspoon salt
6 tablespoons chilled unsalted butter, cut into 1/2-inch cubes
Blend first 5 ingredients in processor. Add chilled butter cubes; using on/off turns, cut in until mixture resembles wet sand.
(After mounding the filling in the crust, pack topping over and around apples. Bake pie on baking sheet in pre-heated 400-degree oven, until topping is golden, about 40 minutes (cover top with foil if browning too quickly). Reduce oven temperature to 350°F. Bake until apples in center are tender when pierced and filling is bubbling thickly at edges, about 45 minutes longer. Cool until warm, about 1 hour. Serve with ice cream.