In a large saucepan melt the butter, a low to medium heat depending on your hob or burner, heat for about ten mins until the butter has a golden to light brown colour, be careful not to burn the butter at this point. Add the vegetarian marshmallows and stir until completely melted. Remove the pan from the heat and stir in the peanut butter until melted. Add the puffed rice cereal, chocolate chips and peanuts. Stir until well coated.
Press the mixture evenly into the prepared baking dish. Cool completely.