In a mixing bowl, whisk together the flour, granulated sugar, brown sugar, cocoa powder, instant coffee and baking powder. Add the buttermilk, vegetable oil and vanilla and mix again until just combined. Pour into the baking dish.
¾ cup all-purpose flour, ⅓ cup granulated sugar, ⅓ cup light brown sugar, ⅓ cup unsweetened cocoa powder, ½ teaspoon instant coffee powder, ½ teaspoon baking powder, ⅔ cup buttermilk, 3 Tablespoons vegetable oil, 1 teaspoon vanilla extract
In a separate bowl, toss together all the topping ingredients except the hot water, then sprinkle over the top of the cake batter. Pour the hot water gently over the top, without mixing into the batter mixture.
½ cup brown sugar, ¼ cup unsweetened cocoa powder, ⅓ cup mini semisweet chocolate chips, 1 ¼ cups hot (not boiling) water