Butter a 9X9 square pan. Set aside.

In a large pot, melt the butter on the stove over medium heat. Add the marshmallows and stir just barely until melted and smooth. Remove the mixture from the heat and stir in the pudding mix. Mix until well combined.

Add the cereal and mix until well coated. Add the extra cup of marshmallows if desired and continue to mix.

Pour the mixture into the prepared pan and gently press down with lightly buttered fingers. Be careful not to press too hard. If you press too hard, the rice krispie treats won't stay as soft and will dry out much faster.

Let the treats sit for about 20-30 minutes before slicing and serving.