Grease and flour an 8-inch square cake pan. In a medium bowl, stir together flour, baking powder, soda, and salt. In a large bowl, beat together sugar and shortening until fluffy. Beat in egg and vanilla. Stir about half the flour mixture into the sugar mixture. Stir in sour cream. Stir in the rest of the flour mixture. Stir in apple and spread evenly into greased pan. Put nuts, brown sugar, butter, and cinnamon into a small bowl and mix until crumbly. Sprinkle over coffee cake. Bake in a 350° oven for 20 to 35 minutes, or until done. Makes 9 servings.