Step 1 In a large saute pan heated over medium heat, melt the butter. Add the rosemary and stir until the rosemary is coated.
Step 2 Stir 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.