Melt the remaining butter in a large pot over medium heat and allow it to brown. It will start to smell toasty and take on a light amber color. Once it does, add the mini marshmallow and salt. Stir until just barely melted; this does not have to be completely smooth and lumps are welcome. Add the cereal and stir well. Transfer the mixture to the prepared dish and press to flatten. The wrapper from the stick of butter or lightly dampened hands are very handy for this. Allow to fully cool and set, then invert the entire pan onto a cutting board. Slice with a sharp knife into neat squares.
