Preheat oven to 350°F. Butter a 2-quart oval casserole dish. In a medium bowl, whisk flour, sugar, baking powder and salt. Whisk in 3 Tbsp. cocoa and 1/2 cup walnuts. Add buttermilk and melted butter, stirring to form a thick batter. Spread batter evenly into prepared pan.
In small bowl, combine remaining cocoa, brown sugar and cinnamon. Sprinkle evenly over batter; top with remaining walnuts.
Pour boiling water in a thin stream over entire surface of brownie; do not stir. Bake until top is set and a bit crispy, 40 to 45 minutes. Serve with whipped cream or ice cream, if desired.
This recipe was easy to make, tasted very good (my hubby loved it!), and still tasted good for sevearl days.
