Heat oven to 350 degrees F. Line a 13x9-inch pan with foil; coat foil with cooking spray.
Melt butter in a small saucepan over medium heat; turn off heat and stir in 2 cups chocolate chips until melted. Add chocolate mixture and pudding mix to a large mixing bowl. Beat until well combined - about 1 minute. Beat in eggs until well combined - about 2 minutes. Beat in sugar and baking soda until well combined. Stir in flour until just combined. Stir in 1 cup cereal and remaining 1/2 cup chocolate chips until combined. Spread batter into prepared pan. Sprinkle with remaining 1/2 cup cereal.
Bake 20-25 minutes, or until well risen and crisp around edges. Cool completely on a wire rack before slicing.