Chocolate-Peanut Butter Bars

These bars are classics of children's cooking adventures and home economics lessons. Try this updated version of the bars, suitable for modern foodies, with your own young chef. Replace the dark sugar with a light brown one if you want a milder one.
Preheat the oven to 350 degrees.Place the first 4 ingredients in a large bowl; beat with a mixer on medium speed until smooth (about 2 minutes). Add the peanut butter, whisking well. Whisk the egg with the egg white.In a dry measuring cup, add flour by weight or lightly spoon; flatten with a knife. Combine flour, baking powder and salt, stirring with a whisk. Gradually add the flour mixture to the peanut mixture, whisking until smooth (the dough should be thick). Spread the dough evenly in a 13-inch x 9-inch metal mold coated with cooking spray.Bake at 350 ° C for 26-28 minutes or until a wooden stick inserted in the middle comes out clean.Place the chocolate in a double boiler set over lightly simmering water; melt the chocolate chips, stirring, until smooth. Spread the chocolate evenly over the top. Cool completely on a wire rack. Cut into bars.