In a large mixing bowl, combine the powdered sugar, creamy peanut butter, softened butter, and vanilla extract. Beat on low speed with an electric hand mixer or stand mixer fitted with the paddle attachment.

Add the milk one tablespoon at a time, mixing after each addition, until a cohesive, slightly sticky dough forms.

Fold ⅓ cup of the mini candy-coated chocolate pieces into the dough with a rubber spatula.

Line a large, rimmed baking sheet with parchment paper or a silicone baking mat.

Portion the dough with a small cookie scoop or tablespoon and roll each portion into a smooth ball.

Place the balls on the prepared baking sheet and freeze for at least 1 hour, or until completely firm.

Place the chocolate chips and oil in a microwave-safe bowl. Microwave in 30-second intervals at 50% power, stirring after each interval, until mostly melted.

Stir until completely smooth and glossy, then let the chocolate cool for a few minutes until warm but not hot.

Dip each chilled peanut butter ball into the melted chocolate, turning to coat completely.

Lift each ball out with a fork, allow the excess chocolate to drip off, and place it back on the prepared baking sheet.

Immediately sprinkle each coated ball with the reserved 3 tablespoons of mini candy-coated chocolate pieces.

Refrigerate for at least 1 hour, or until the chocolate coating is completely firm. Serve chilled.