1/3 cup butter; softened
1 cup sugar
2 large eggs
1 teaspoon vanilla extract
1/3 cup unbleached all-purpose flour
1/4 cup semi-sweet chocolate chips

Preheat the oven to 350°F. Spray an 8-inch square baking pan with non-stick spray.

In a mixing bowl, cream the eggs and butter until light and fluffy. Beat in the eggs and vanilla, blending well. Add the flour and beat until smooth. Pour half of the batter into the pan and set aside.

Melt the chocolate chips in the microwave or a double boiler, or over very low heat. Add the melted chips to the remaining batter, blending well.

Spread the chocolate batter over the white batter in the pan. Slice a zigzag pattern through the batter, using a spatula, through the layers to marble the dark with the light.

Bake for about 25 minutes.

Place the pan on a wire rack to cool until cold to the touch, before cutting into squares.

About 8 servings.