Step 1

Prepare a 9x13-inch pan by lining with a parchment paper sling or generously butter the bottom and sides.

Step 2

Melt the butter (save the wrappers for pressing the rice krispie treats into the pan) in a large pot over medium-high heat.  Once it melts, keep watching it and it will bubble, then foam, then eventually turn a dark golden brown color and smell nutty.  Watch carefully though, because it can go from golden brown to burned very quickly.  Little bits of brown sediment in the bottom of the pan are fine though.

Step 3

As soon as the butter is browned, turn off the heat and add all but 3 cups of the marshmallows.  Stir the butter and marshmallows together with a long-handled wooden spoon until the marshmallows are melted.  There should be enough residual heat from browning the butter to melt the marshmallows completely, but if not, return the pot to low heat to fully melt the marshmallows.

Step 4

Add the Rice Krispies, 3 cups of reserved marshmallows, and coarse salt and stir until combined.  Gently press into a prepared 9x13-inch pan using the reserved butter wrappers.

Step 5

Let the rice krispies cool for an hour before slicing.