In a bowl stir brownie mix and all ingredients called for on the box.
Spread ½ the batter in the prepared baking dish. Lay chocolate bars on batter; they should exactly fit into the dish. Cover bars with remaining brownie batter, using the back of a spoon or a spatula to spread evenly.
All chocolate bars should be covered, although it will look like a thin layer. Bake for 30 minutes. Remove from the oven and cool the pan on a rack.
