Congo Bars

Preheat oven to 350°. Lightly grease a 9 x 13-inch baking pan with butter or vegetable oil.

Blend the flour, baking soda and salt in a small bowl with a wooden spoon.

Using an electric mixer on medium speed, cream the butter, sugar and vanilla in a medium-size bowl until light and fluffy, about 2 minutes.

Stop the mixer once or twice to scrape the bowl with a rubber spatula.

Add the eggs and mix on high speed for 3 seconds, then on medium speed until blended, about 5 seconds.

Add the flour mixture and mix on low speed until almost blended, 8 to 10 seconds.

Stop the mixer once to scrape the bowl.

Add the chocolate chips and nuts and mix on low speed for 5 seconds.

Finish the mixing by hand with a wooden spoon.

Spread the batter evenly in the prepared pan.

Bake the bars on center oven rack until the top has formed a rich, golden crust and dropped below the level of the darker golden outer edges, 30 minutes.

These bars cannot be tested by inserting a tester because the inside remains gooey.

Cool 30 minutes in the pan, placed on a rack before cutting.