Step 1In the bowl of a stand mixer fitted with the paddle attachment, beat the peanut butter and the butter until smooth. Add the powdered sugar and beat until smooth.
Step 2Place the crisped rice cereal in the bowl of a food processor and crush to a very fine meal. Add the cereal to the peanut butter mixture and beat to combine. This makes about 3 cups filling. Cover and refrigerate until very firm, 3 to 4 hours.
Step 3Divide the filling into generous 1-tablespoon scoops. Very quickly, roll the scoops into balls, then flatten slightly to form patties about 1 inch wide by ½-inch thick. If the dough begins to warm and get sticky, freeze the scoops until firm enough to mold. Freeze the formed patties, uncovered, on a parchment-lined baking sheet until solid, preferably overnight.
Step 4Melt the chocolate chips in a large microwave-safe bowl, stirring every 20 to 30 seconds until evenly melted. If the melted chips feel a little too thick, stir in a little coconut oil to thin the melted chocolate.
Step 5Remove just a few patties at a time (keep the rest of the patties frozen), and dip them, one at a time, in the melted chocolate. Tap the candy a few times to remove excess chocolate and carefully drop each piece into a candy or truffle paper cup, adjusting the sides as needed so the patty sits level in the cup. Repeat until all of the peanut butter cups are assembled.
Step 6Place the cups in the refrigerator until the chocolate is hardened before serving.