1. Preheat oven to 350 degrees F.
2. Crust: In small bowl, mix together butter, 1/2 cup brown sugar and 1 cup flour until crumbly. Pat dough into greased pan (8-inch square or 9-inch square). Bake at 350 degrees F for 20 minutes.
3. Topping: In small bowl, mix together brown sugar, eggs, salt, vanilla, flour and baking powder. Stir in coconut and chopped nuts.
4. Assemble and bake: Pour topping over baked crust. Return to oven (350 degrees F) and bake for about 30 minutes.