1Heat oven to 350°F. Grease 9-inch square pan with shortening or cooking spray. In large bowl, beat 1 1/2 cups of the brown sugar and 1/2 cup butter with electric mixer on medium speed 2 minutes or until creamy. Beat in egg. In small bowl, mix 2 cups of the flour, the baking powder, allspice and salt with whisk. On low speed, add flour mixture to butter mixture, beating just until blended; fold in sour cream and apples. Spread batter in pan.
2In small bowl, mix remaining 1/2 cup brown sugar and 1/2 cup flour. Stir in 6 tablespoons butter with fork until mixture looks like fine crumbs. Stir in pecans. Sprinkle crumb topping over batter.
3Bake 55 to 60 minutes or until toothpick inserted in center comes out clean. Cool in pan on cooling rack 1 hour. Serve slightly warm.