Grease a 9- x 9-inch pan. 

Melt butter in a large saucepan over medium heat. Cook for 5 to 7 minutes, or until melted butter is nut brown in color and very fragrant.

Reduce heat to medium low, and add maple syrup (the mixture will bubble up). Add salt, vanilla, and marshmallows; stir until melted. 

Pour in cereal, stirring to coat. Turn out mixture into prepared pan. Press down with a piece of greased parchment paper or lightly buttered hands. Cool before cutting into squares or your favorite shapes.