In a medium saucepan over medium heat, melt the butter. Add marshmallow cream and stir until smooth and well combined. Remove from heat.
Add ground pecans and half the cereal. Stir to coat cereal. Add other half of dry cereal and mix well.
Press into an 8 x 8-inch or 9 x 7-inch ungreased glass baking pan. Top with pecan halves if desired. Let set up for at least an hour before cutting.