Follow instructions on Marshmallow bag for Rice Krispies Treats. Reserve 10 mini marshmallows for later. Mold the Rice Krispies into balls. Cut the reserved marshmallows in half; add one half to the top of each ball. Secure the marshmallow with two toothpicks.
Stir oil into white chocolate morsels in a glass bowl. Melt chocolate in the microwave on high in 15 second intervals, stirring well after each interval. Continue until chocolate is warm, and completely melted.
Line a baking sheet with parchment paper; place cookie drying rack over cookie sheet. Pour melted chocolate over the top of the Rice Krispies Ornament Treat. Pinch the toothpick ends to lift it up; gently tap-drop the ball a few times over the rack to spread the chocolate. Use a spoon to add more to the base if it isn't completely covered.
Allow to dry completely before removing the toothpicks. Decorate with royal icing if desired.
Prep and cooking times will vary depending on how many you make.