Preheat oven to 350 degrees. Grease a 9-inch-by-12-inch baking pan well with butter. Set the pan aside.
Melt the 2 sticks of butter in a 2 quart microwave-safe bowl covered with a paper towel. Remove the bowl from the microwave, and add the brown sugar. Stir well. Add the baking powder, salt and vanilla extract, stirring until completely incorporated. Stir in the flour, again stirring until it is well mixed.
Crack the eggs into a small bowl, and beat them well with a fork or whisk. Add the eggs to the batter and stir with a spoon until they are completely incorporated. Stir in the chocolate chips (and nuts, if using).
Spread the batter in the greased pan. The batter will be stiff and sticky. You may have to spread it with the back of a spoon, but don't worry too much about getting it exactly even, as the batter will spread as it bakes.
Bake until the top begins to get golden brown and the blondies just begin to pull away from the sides of the pan, 20 to 25 minutes. (Baking time will vary depending on your oven and the type of pan.) Do not overbake. Cool for at least 20 minutes, and cut into small squares. (4×6=24) Store in an airtight container or cover well with plastic wrap. These bars freeze very well and improve in flavor after the first day.
Makes 2 dozen
Note: To get the proper texture, do not use an electric mixer.
Start to finish: 7 minutes preparation, plus approximately 20-25 minutes baking time and 20 minutes cooling time.
Per Blondie: 216 calories (41% from fat), 10 g fat (6 saturated), 38 mg cholesterol, 2 g protein, 31 g carbohydrates, 1 g dietary fiber, 59 mg sodium.