Directions

1. Spray 8-inch square baking dish with cooking spray. In a medium bowl sift together flour, cocoa, salt, and espresso.
   
2. Place chocolate chips and butter in a bowl and microwave for 1 minute, stir. Microwave in 30-second intervals, stirring after each interval, until fully melted, about 2 minutes, set aside. Preheat oven to 350 degrees.
   
3. In the bowl of an electric mixer with paddle attachment beat eggs and sugar on medium-high speed until pale and doubled in volume, about 2 minutes. Beat in flour mixture on low speed until just combined, about 30 seconds. Gradually beat in melted chocolate mixture just until no streaks of chocolate remain, 1 minute.
   
4. Pour half of batter into prepared baking dish. Dollop peanut butter evenly over batter. Top with remaining batter. Sprinkle with peanuts.
   
5. Bake in preheated oven until edges of cake start to pull away from sides of baking dish and center still jiggles slightly, 30-35 minutes. Serve immediately with vanilla ice cream, if desired.