Preheat oven to 350°F (175°C). Grease an 8x8 inch baking pan.
In a medium saucepan, melt the butter. Remove from heat and stir in cocoa powder and sugar until blended. Add eggs, one at a time, mixing well after each addition. Stir in vanilla.
In a small bowl, combine the flour, baking powder, and salt. Gradually stir the dry ingredients into the cocoa mixture.
Stir in the walnuts and chocolate chips.
Spread evenly into the prepared pan.
Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Let cool before cutting into bars.
Interesting Facts
Brownies are believed to have originated in the United States in the late 19th century.
The first published recipe for brownies was in the 1906 version of the Fannie Farmer Cookbook.
The first known recipe for a brownie with walnuts dates back to the 1920s.