In a large pot, melt butter over medium heat until completely melted. If you want to brown butter, let it melt until it starts to foam and becomes a golden amber color. Watch carefully.

Once butter is melted, stir in marshmallows, reserving 2 cups to add later. Continue to stir often as marshmallows begin to melt.

Once marshmallows are melted, remove from heat. Stir in vanilla and stir to combine. Add rice krispies cereal. Fold the mixture well to ensure all ingredients are incorporated. Add remaining 2 cups of marshmallows and fold together.

Spread in greased or foil-lined 9 x 13 pan. If you desire a thicker bar, use a 9-inch square pan. Let bars sit for 10-20 minutes. Cut into squares.

If you want to dip into milk, semi-sweet, or dark chocolate, it is very easy. Simply melt the chocolate of choice in a microwave at 50% power or over a double boiler. Dip rice krispie treats in chocolate and let firm up on a cooling rack or parchment lined baking pan.