In a large saucepan, melt butter over low heat, stirring continuously to prevent burning. Once melted, add marshmallows and stir until fully melted and smooth, about 3-5 minutes.

Remove from heat, and add puffed rice cereal to the melted marshmallow mixture. Fold until each piece is coated, about 1-2 minutes.

Let the mixture cool for about 5 minutes. Grease hands to prevent sticking, then scoop and roll into 1-inch balls, placing them on a parchment-lined tray.

Melt the white chocolate in a microwave-safe bowl in 30-second bursts until smooth. Dip each rice crispy ball into the chocolate and roll in sprinkles before the chocolate hardens.

Place the chocolate-coated balls back on the tray and let them set for about 30 minutes at room temperature, or refrigerate for quicker setting.