01 -
Smear mayo on the outer sides of bread, add mustard inside one piece. Pile your cheeses on the mustard-covered side.
02 -
Get your skillet warm on medium-low, drop in butter till it coats the surface.
03 -
Pop a lid on and let it cook for 2-3 minutes until you see a nice golden color.
04 -
Turn it over, keep covered for another 1-3 minutes till golden and cheesy inside. Lower the heat if it's browning too quickly.