Melt butter over low heat. Add marshmallows and stir until completely melted.
Stir in Rice Krispies® until well coated. Press into a well-greased 9x13 baking dish. Allow to cool completely. Cut into 12 bars.
Melt white chocolate according to package directions. Using the white chocolate, adhere various bunny decorations as desired. Allow to cool completely on the counter, or place in the refrigerator for quick cooling.