Combine cocoa powder and confectioners' sugar in a shallow bowl; set aside.

Place peanut-butter chips in a heat-proof bowl. In a saucepan, bring cream and vanilla extract to a simmer over low heat. Pour over peanut-butter chips. Stir until chips are completely melted and blended in. Let the mixture cool until it is just slightly warm to the touch.

Add butter, stirring until melted and well-blended. Cover with plastic wrap and refrigerate for at least 1 hour.

Scoop peanut-butter mixture by teaspoonfuls and roll into balls. Roll each ball in cocoa mixture and place on a cookie sheet covered with waxed paper or parchment paper. Cover with plastic wrap and refrigerate until firm.