Cake:

2 cups all-purpose flour

1 cup granulated sugar

1 T. baking powder

1 teaspoon salt

5 T. softened butter

1 cup milk

1 large egg

Bottom Layer of Cake:

1/4 cup butter

½ cup brown sugar

2 medium baking apples

Streusel Topping:

1/2 cup light brown sugar, packed

1/2 cup chopped walnuts

1/4 cup all-purpose flour

1/2 teaspoon ground cinnamon

Heat the oven to 350° F.  Make the topping.  In a bowl, combine brown sugar, chopped pecans or walnuts, flour, and cinnamon. Add the butter and mix with a fork until the mixture is crumbly. Set aside.  Make the bottom layer.  Put the butter in a 9-inch square pan. Put it in the oven until the butter is melted.  Meanwhile, peel and core the apples. Slice the apples in thin wedges.  Remove the pan from the oven and sprinkle the butter with the brown sugar. Arrange apple slices evenly over the butter and brown sugar layer.  Make the cake.  In a large mixing bowl, combine the flour, granulated sugar, baking powder, salt, butter, milk, and egg. Beat on low speed with an electric mixer until combined, then beat on medium speed for 2 minutes. Scrape the sides of the bowl occasionally.  With a spoon, dollop the cake batter evenly over the apples, then carefully spread the batter to cover. Sprinkle the streusel mixture evenly over the top of the batter.  Bake the coffee cake for about 45 to 50 minutes, or until a wooden toothpick or a cake tester inserted in the center comes out clean.  Immediately invert the cake onto the platter or pan and leave for a minute.  Remove the baking pan. If any apples and syrup are stuck in the baking pan, scrape them out onto the cake.