Step-by-Step Instructions
First, we build our flavor foundation: the onions. In your large skillet or pot, melt the butter with the olive oil over medium-low heat. Add all those sliced onions and sprinkle with the sugar and a pinch of salt. This is where patience is key. Stir them occasionally, letting them soften and slowly turn a deep, golden brown. This took me a full 25-30 minutes, and I learned the hard way that cranking up the heat just burns them. You’ll know they’re ready when your entire kitchen smells incredible and they’re jammy and reduced.
While the onions are caramelizing, I brown the ground beef in a separate pan until it’s just cooked through, then drain any excess fat. Once the onions are perfect, push them to the side and add the garlic, thyme, salt, and pepper right into the center of the pan for a quick, fragrant 60-second cook. Sprinkle the flour over everything and stir for another minute—this is our thickener. Then, slowly pour in the beef broth and Worcestershire sauce, scraping up any browned bits from the bottom of the pan. That’s pure flavor!
Now, stir in the uncooked rice and the browned ground beef. Bring it all to a gentle simmer. Here’s my trick: I turn off the heat, stir in one cup of the Gruyère and all the mozzarella until it starts to melt into the saucy mixture, creating a creamy base. Then, I smooth the top and blanket it with the remaining Gruyère. Cover the skillet tightly with foil and bake at 375°F (190°C) for 25 minutes. Then, I remove the foil and bake for another 10-15 until the top is gorgeously bubbly and golden.
Pro Tips for Best Results
I tested the onion-caramelizing step three different ways: high heat for speed, adding broth early, and the low-and-slow method. The low-and-slow method won by a mile. It coaxes out the onions’ natural sugars without any bitterness. If you see them sticking, add a tiny splash of water, not more oil. This patience transforms the entire dish from good to “can I have the recipe?” level.
Please, I beg you, grate your own cheese. I’ve used pre-shredded bags in a pinch, but they contain anti-caking agents that prevent them from melting as smoothly and can leave a grainy texture. Taking two minutes to grate a block of Gruyère and mozzarella results in a velvety, unified cheese sauce within the casserole and a perfectly melted top. It’s a simple step with a massive payoff.
Let the casserole rest for 10 minutes after pulling it from the oven. I know it’s hard to wait when it looks and smells so good, but this is crucial. This resting time allows the rice to fully absorb any remaining liquid and the whole dish to set up, so you get clean slices instead of a soupy scoop. It also saves the roof of your mouth from a scalding-hot cheese burn!
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