Prepare a 9x13 baking dish by spraying with nonstick spray
In a large pot melt the butter over low heat.
Stir in the vanilla extract.
Add in the marshmallows and stir continuously until they have melted.
Stir in the rice krispie cereal until coated with the marshmallow cream.
Spoon the coated rice krispies into the prepared baking dish and gently press down to spread the mixture.
Allow the rice krispie mixture to cool for 30 minutes.
Using a spatula gently loosen the edges of the treats. Turn the dish over onto a clean cutting board. Use a large knife to trim the edges so they are straight. Set aside the trimmed pieces.
Cut the block of treats down the middle the long way. This will split the treats into two pieces.
Cut each section on an angle to form triangle shaped pieces.
Place the white chocolate melts into a microwave safe container. Follow the directions for your brand of white chocolate melts. If they do not have directions, then microwave for 1 minute at 50% power or on the defrost setting. Stir well. If not melted place in microwave for 30 seconds and stir again.