1/4 cup butter or margarine
1 cup firmly packed brown sugar
1 large egg
1 teaspoon vanilla extract
1 teaspoon baking powder
1/4 teaspoon salt
About 1 cup all-purpose flour
1 cup semisweet chocolate chips
3/4 cup coarsely chopped walnuts

In a 2- to 3-quart pan over medium-high heat, melt butter until it begins to brown, 3 to 5 minutes (if using margarine, melt but do not brown). Let cool for 20 to 25 minutes.

Add sugar, egg, vanilla extract, baking powder and salt; stir to mix well. Add 1 cup flour and stir until incorporated; mixture will be stiff. Stir in half the chocolate and half the nuts.

Butter and flour an 8-inch square pan. Spread batter level in pan; sprinkle with remaining chocolate and nuts.

Bake at 350 degrees F until edges begin to pull from pan sides and brownies are firm to touch in the center, about 30 minutes (25 minutes in a convection oven).

Cool in pan on a rack at least 30 minutes. Cut into 8 equal pieces. Serve warm or cool.