6 Tb unsalted butter -- room temperature
1/2 Cup nutty old-fashioned-style
or freshly ground peanut butter
1 1/4 Cups golden brown sugar -- packed
2 Large eggs
2 Tsp vanilla extract
3/4 Cup all purpose flour
1 Tsp baking powder
1/4 Tsp salt
4 Ozs bittersweet chocolate or semisweet chocolate-- coarsely chopped

Preheat oven to 350ºF. Generously butter and flour 8-inch square baking pan. Using electric mixer, beat butter in large bowl until smooth. If oil has separated from peanut butter, stir to blend. Add peanut butter to butter; beat until well blended, scraping down sides of bowl occasionally. Beat in brown sugar. Add eggs 1 at a time, beating well after each addition. Beat in vanilla.

Sift flour, baking powder and salt into medium bowl. Add to peanut butter mixture; beat until blended. Stir in chocolate. Transfer batter to pan. Using spatula, smooth top.

Bake until toothpick inserted 2 inches from edge of pan comes out with moist crumbs attached, about 33 minutes. Transfer pan to rack and cool completely. (Can be made 3 days ahead. Cover; store at room temperature.) Cut brownies into squares.