Step 1In a large saute pan heated over medium heat, melt the butter. Add the rosemary and stir until the rosemary is coated.
Step 2Stir in the marshmallows, and continue to stir until the marshmallows melt and mix with the butter, about 5 minutes.
Step 3Stir in the vanilla and salt, then slowly stir in the cereal until it is evenly coated. Remove the pan from the heat.
Step 4Transfer the mixture to a shallow 9-by-13-inch baking pan. Cover the top with parchment paper, pressing down firmly to level off.
Step 5Set the pan aside for at least 1 hour to cool before slicing into squares.