Heat the oven to 375 degrees F. Butter a large baking dish and set aside. Place the apples, lemon juice and vanilla in a large bowl and toss to coat. Add the granulated sugar, 1 1/2 tablespoons flour and nutmeg, stirring to combine.
Place remaining 1 cup flour, nuts, brown sugar, cinnamon and salt in a medium bowl. Using a pastry cutter or 2 knives, cut the butter into the flour mixture until it resembles coarse crumbs. Sprinkle the mixture over the apples. Bake until golden brown, about 40 minutes. Serve warm with ice cream.