1Heat oven to 350ºF. In ungreased square pan, 9x9x2 inches, mix flour, granulated sugar, 2 tablespoons cocoa, the baking powder, salt and 1/4 teaspoon cinnamon. Stir in milk, oil and vanilla with fork until smooth. Stir in nuts. Spread evenly in pan.
2In medium bowl, mix brown sugar, 1/4 cup cocoa and 1/4 teaspoon cinnamon; sprinkle over batter. Pour boiling water over batter.
3Bake cake 40 minutes. Let stand 15 minutes. Spoon cake with sauce into individual dishes. Top with ice cream.