Take the butter out of the fridge to let it soften. Preheat over to 350F and move the rack to the top third of the oven. Line a baking sheet with tin foil for easy clean-up.
Slice the bread one way (without cutting through completely), then slice it the other way to make a criss-cross pattern of cuts.
Prepare the cheeses.
Make the garlic butter by mashing the butter, minced garlic, parsley, and salt and pepper together with a fork.
Coat the inside of the cracks with the garlic butter (I used a fork), then stuff with the cheeses (doesn't matter which order... it'll all melt together anyway).
Place the loaf on the baking sheet. Loosely cover it with a piece of foil, and place it in the oven. After 15 minutes, remove the foil and bake for another 15 minutes. If desired, broil for an additional minute or two.