1 oz. semisweet chocolate
1 oz. unsweetened (baking) chocolate
1 T. unsalted butter
1/3 C. creamy peanut butter, preferably natural
2 T. canola oil
1/2 C. firmly packed brown sugar
1/2 C. sugar
2 large eggs
1 1/2 t. vanilla extract
3/4 C. flour
1/4 t. salt
Heat oven to 325° F. Butter an 8-inch square baking pan (or coat with nonstick cooking spray).
In a microwave-safe glass bowl, melt both chocolates with the butter on high for 1 minute. Stir and cook another 30-60 seconds.
Set aside to cool slightly.
In a medium-size bowl, beat the peanut butter and the oil. Add brown sugar and white sugar; continue beating until the mixture is light and fluffy. Add the eggs, one at a time, beating well after each addition.
Mix in the vanilla extract, then the flour and salt until just combined.
Stir 1/3 cup of the peanut butter batter into the chocolate mixture. Scrape the remaining peanut butter batter into the baking pan. Spoon the chocolate mixture over the batter.
Using a table knife, make a zigzag through the layers to create a marbled effect.
Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out almost clean.
Cool in the pan, then cut into 16 bars. Store in an airtight container at room temperature.
Yields 16 servings.