Beat together butter, cream cheese and brown sugar until it is fluffy. Add pumpkin and continue beating until blended. Add eggs, beating well after each egg.
In another bowl combine flour, baking powder, salt, and spices. Slowly add this to the wet mixture and use a whisk to stir. Mix until just blended, then pour into crust.
For the topping: combine 2/3 c flour, 1/3 c nuts, 2/3 c brown sugar and 1/4c melted butter. Crumble the topping over the filling.
Bake at 350 for 45 minutes. Allow to cool completely before slicing. Refrigerate for a firmer texture.