Preheat an oven to 425°F.
First up, trim the cauliflower. Depending on where you bought it and how trimmed it already was, this step may take different forms. In short, you want to remove any excess stem and at leaves, if there are any, from the cauliflower. Cut out the core of the cauliflower. You may be tempted to discard it, but I encourage you to slice it (about 1/4-inch-thick) and roast it up along with the florets. Divide the cored head into florets—pulling them apart where they naturally break and cutting larger ones up from the core of the solid part and into the floret to help it “break” naturally. Or, you can keep things simple and just cut the entire head into 3/4-inch thick slices. The slicing method yields several "steaks" of cauliflower and a bunch of smaller pieces that break off.
Decide if you want to peel the garlic or not. For soft and mellow garlic, leave them peeled and just remove as much excess papery peel as slips off easily. For crunchier cloves, peel them before roasting.
Put the prepped cauliflower and garlic cloves in a pile on a baking sheet (line it with parchment paper or foil for easier clean up). Drizzle everything with the olive oil. Use your fingers to coat everything with the oil, turning over all the pieces so everything is more or less coated with the oil. (Yes, you could do this in a bowl and toss everything using a spatula or a spoon to keep your hands clean, but you’d have another bowl to wash—your choice!) When everything is lightly coated, spread it all into a single layer.
Sprinkle with the salt and pepper—feel free to use more or less according to your taste—and roast until the cauliflower is just tender, about 30 minutes.
Remove the pan from the oven. Use tongs or a fork to turn over all the cauliflower pieces and move them around a bit. Sprinkle the whole thing with the Parmesan and bake until the cheese is melted and the cauliflower is truly and completely tender, 5 to 10 minutes. If things aren’t as brown as you’d like at this point, go ahead and run it under a broiler for a minute or two if you’re so inclined.