To brown the butter, add it to a large saucepan over medium heat. It will melt and begin to bubble. Stirring the whole time, let it cook until it begins to foam up and you can smell a nutty smell and see a brown color. It should take about 5 minutes.
Immediately add the marshmallows and cook until they are melted and combined with the butter.
Take off the heat and add the vanilla and the Cinnamon Toast Crunch. Press into a 9x13 inch pan and let it cool off. Once it is cool, cut it into slices and enjoy!