Preheat a cast iron skillet on medium low while lightly buttering two slices of bread on one side each. In the skillet, place the butter sides down into the pan and spread about 1 1/2 Tbs of pesto on each side. Divide about 1/3 C (33g) of cheese total, between both slices of bread. With both slices of bread, cheese side up, grill on medium-low with lid on for four minutes (set a timer). Remove from heat and let sit, lid on, for an additional three minutes (again, set a timer) - but check after two minutes just to make sure the toast isn't too toasty!