Over time the grilled cheese sandwich has grown up and evolved. I think it’s safe to say it’s been perfected.
Caramelizing onions to a golden brown perfection is a labor of love. It to will not be done quickly. They can be done ahead of time. Used in sandwiches, soup, scrambled eggs, or onion dip. Sauté stirring frequently low and slow. I like to add a combo if olive oil and butter about a Tbs of each per onion. It may seem like forever 30-40 minutes before they start to brown. Don’t crowd the pan or they will steam and take even longer to brown. Once they start to brown keep going about 10 minutes longer to get the deep golden color. You’ll be happy you did.
Find it online: https://www.tableanddish.com/grown-up-grilled-cheese/