Preheat oven to 350°.

Butter and flour a 13x9 inch baking pan.

The topping: combine the butter, brown sugar, and pumpkin pie spice in a big bowl.

With 2 knives, cut in the butter.

Add in the flour and pecans; using your fingers, blend the flour and butter together to make large crumblike pieces.

Add in the chocolate chips and quickly work them into the topping.

The cake: sift the flour, baking powder, baking soda, salt, and pumpkin pie spice onto a large sheet of wax paper.

In a mixing bowl, beat the butter with an electric mixer on medium speed until light and fluffy.

Gradually add the sugars, continuing to beat until very light.

Add the eggs one at a time, beating well after each addition.

With the mixer on low speed, alternately beat in the flour mixture and the buttermilk, beating until the batter is just mixed.

Add in the vanilla and mix.

Spread the batter evenly in the prepared pan.

Evenly sprinkle with the crumb topping, pressing it gently into the batter.

Bake 40-45 minutes, or until the top of the cake is firm and the streusel is crisp and bubbling.

A pick inserted into the center should come out clean.

Let cool slightly in the pan on a wire rack.

Serve warm, cut into squares.