Chocolate Rice Krispies

5 tablespoons unsalted butter
3 tablespoons light butter
1/3 cup unsweetened cocoa powder
2 bags (10 ounces each) mini-marshmallows
10 cups crisp rice cereal
1/2 cup semisweet mini chocolate chips
Vegetable oil cooking spray

Combine butters and cocoa in a large saucepan over medium-high heat. Melt butter, whisking until mixture is well combined. Stir in marshmallows, melting them completely. Remove pan from heat and stir in cereal, working quickly before marshmallow mixture sets. Stir in chocolate chips. Coat hands with cooking spray and shape mixture into about 80 walnut-sized balls. Place balls on a baking sheet and let harden for about an hour. Store in an airtight container in a cool, dry place for up to 3 days. (Do not refrigerate.)