Nonstick pan spray
1⁄3 cup semisweet chocolate chips
1 tablespoon unsalted butter
¼ teaspoon salt
2 tablespoons plain nonfat Greek-style yogurt
1 tablespoon liquid egg substitute
½ teaspoon pure vanilla extract
¼ cup unsweetened Dutch-processed cocoa powder
1 tablespoon all-purpose flour
2 egg whites from large eggs
1⁄3 cup sugar
4 teaspoons reduced-fat peanut butter, smooth or chunky, preferably natural style