Cinnamon Streusel Coffee Cake

2 cups flour
1 cup sugar
1 cup buttermilk
2/3 cup oil
1 tsp baking soda
2 tsp baking powder
1/2 tsp salt
2 eggs
1/2 cups brown sugar

TOPPING:
1/2 cups brown sugar
1 stick butter, melted
1/2 cup walnuts, chopped
1 tbsp cinnamon

Preheat oven to 400 degrees. Spray 9 inch deep dish baking pan/stone with cooking spray.
Mix together all ingredients for cake until batter is smooth. Pour into stone.
In another bowl, mix together ingredients for topping, until well crumbled. Sprinkle over cake.
Bake35-40 minutes or until toothpick stuck in middle comes out clean.