Ingredients
Equipment
Method
- Preheat the oven to 400˚F. Butter a 9x13 baking dish on the bottom and sides.
- Slice the onions ½ inch thick, then separate each slice into individual rings. Keep the rings whole as much as you can, but a few broken ones are fine.
- Whisk the beef base into the melted butter until smooth. To a very large bowl, add the onion rings and the butter mixture and toss until every ring is coated. Sprinkle the thyme, parsley, oregano, dry mustard, smoked paprika, garlic powder, salt, pepper and cayenne over the top. Set a second bowl of about the same size upside down over the first and shake until the onions are evenly coated.
- Arrange the rings in the buttered dish so they lie mostly flat and intact. They don't need to be in perfect rows, but don't pile them in a heap.
- Roast, uncovered, for 35 to 40 minutes, until the onions are very soft and starting to color at the edges. If they begin to brown too quickly, lay a sheet of foil loosely over the top for the remaining time. (The goal is to drive off moisture, so don't crimp the foil tightly.)
- Remove the dish from the oven. If there is liquid pooled in the bottom, sop it up with paper towels. Too much liquid will make the cheese gummy underneath.
- Scatter the mozzarella and cheddar over the onions, then the Parmesan. Bake for 15 to 20 minutes, until the cheese is melted and just starting to brown.
- Switch the oven to broil and broil until the top is deep golden brown and bubbling, watching closely the whole time. Let rest for 5 minutes before serving.
Notes
Onions: Slice a full ½ inch thick and keep the rings intact. Thinner rings fall apart and turn to mush.
Foil: Only cover during the first roast if the onions are browning too fast, and lay the foil on loosely. A tight cover traps steam, which is what causes the puddle.
Blot: Don't skip the paper towels after the first roast. This is what keeps the cheese melty instead of gummy.
Cheese: Shred from a block if you can. Gouda or Gruyère can replace the mozzarella.
Make it vegetarian: Leave out the beef base and whisk ½ teaspoon of vegetable base into the butter instead, or add an extra ¼ teaspoon of salt.
Storage: Refrigerate leftovers in an airtight container for up to 4 days. Reheat at 350˚F for about 15 minutes, until the cheese is bubbly. We don't recommend freezing.