Creamy Baked Double Cheese and Onion Dip (gluten-free)

"This dip is pure, unadulterated comfort food. It's fattening, full of sodium, creamy and rich, with some soft texture from the onions, and a tiny bit of heat to keep you going back for more. It's dangerously easy to make and addictively good. The more you have, the more you'll want. I used light cream cheese and mayo; use light or regular. I grated a block of gouda cheese, but any cheese from Parmesan to a 4-cheese blend will be lovely. Optionally, you could add in a couple handfuls of frozen spinach and artichokes, or corn, beans, or pre-cooked rice to beef it up. It's perfect for football or sports parties, as an appetizer at any dinner party, as a holiday side dish, or make it just because. Leftovers reheat well in the micro. Although I haven't tried it, you could probably use vegan products for the cheese, cream cheese, and mayo...."