Get together your equipment: skillet, metal spatula, saucepan lid (a Revereware saucepan lid is what we've always used, as it's the perfect size).
Evenly spread a teaspoon of butter on each side of both pieces of bread.
Spread 2 teaspoons of peanut butter on one side of each piece of bread.
Place the cooked bacon on one of the pieces of bread, then cover it with the other slice so that the bacon is sandwiched by the peanut butter.
Heat up a skillet over medium temperature, and when it is hot place the sandwich in; push the bread down a little with a metal spatula, then cover the whole thing up with the saucepan lid (the idea is to heat the air underneath the lid and warm the peanut butter up as you're also browning the bread).
Uncover every minute and check the cooking bread color- you want it golden, not burnt.
When it's to the color you like, carefully flip the sandwich over, press down on it with the spatula to squish the bread, peanut butter, and bacon together, and re-cover with the saucepan.
After about 3-5 minutes of slow cooking, you'll have a wonderfully golden, melty, gooey grilled peanut butter and bacon sandwich!