Line a 9 x 13 baking pan with parchment paper. You can use a larger pan if you prefer smaller treats.
Heat the butter over medium heat until it starts to brown and give a light nutty scent. Remove from heat immediately to prevent the butter from burning.
Add the vanilla and salt to the butter and mix.
Add the marshmallows and mix until they are mostly melted. The heat of the pot and the butter should be enough to melt the marshmallows. If not, put the pot back on the burner and put the heat on low until the marshmallows melt.
Add the Rice Krispies one cup at a time and mix thoroughly.
Pour the mix into the pan and pat down until flat. Allow to cool - about 1 - 2 hours. Cut into squares
Do not press down too firmly on the treats when adding them to the pan. Store in an airtight container for up to a week.