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You know how sometimes you just need dinner to feel like a warm blanket — nothing fancy, just something that fills your belly and calms your nerves? That’s exactly what this casserole is for me.
I first made it on one of those evenings where the fridge was looking half-empty, the day had run long, and I honestly didn’t have the energy for “real cooking.” I had some cooked rice, mushrooms that were hangin’ on for dear life in the crisper drawer, and a block of white cheddar begging to be used.
Thirty minutes later, I had a bubbly, golden-topped casserole that tasted like it should’ve taken hours. My husband even paused the TV to ask, “What is this? It’s amazing.” That’s how I knew I’d struck gold.
Why You’ll Want This in Your Back Pocket
Let me put it plain:
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It’s hearty — like stick-to-your-ribs but not heavy-you-down kind of hearty
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Uses up leftovers — that cold rice from takeout? Perfect for this
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Cheesy but not too cheesy — it’s rich, not greasy
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The mushrooms bring that earthy umami magic
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You can prep it earlier and bake it when you’re ready
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Great for picky eaters, vegetarians, or anyone needing comfort food
Ingredients (With a Little Sass & a Few Swaps)
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6 tbsp unsalted butter, split in half. First half for cooking, second for thickening.
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1 small onion, finely chopped. I won’t tell if you use pre-chopped from the freezer.
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8–10 oz mushrooms, roughly chopped. Use what you’ve got — cremini, maitake, even a mix of fresh and dried.
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3 tbsp all-purpose flour — this is your thickener for the creamy sauce.
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2 ¾ cups whole milk, room temp. 2% is fine if it’s what you’ve got.
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1 tsp dried thyme
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¾ tsp ground nutmeg — just trust me. It gives a warm, cozy flavor.
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½ tsp dried sage
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4 cups cooked white rice — cold, day-old rice actually works best here.
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1 ¾ cups shredded white cheddar, divided. Go for sharp cheddar if you want that little tang.
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Salt & pepper, to taste — and don’t be shy with that black pepper.
Let’s Cook — Step by Step, No Stress
1. Set the Scene
Turn that oven on to 350°F. Grease a 9×9 dish (I use baking spray, but butter works fine), and put it on a foil-lined baking sheet — it keeps any cheesy spills from burning on the bottom of your oven. Learned that one the hard way.
2. Start with the Good Smells
Melt 3 tablespoons of butter in a medium saucepan over medium heat. Add in your chopped onion and cook it slow and steady for 8 to 10 minutes, until it softens and starts to go see-through. You’re not looking for color — just that gentle sweetness.
Toss in the mushrooms and cook those babies down for about 4 to 5 minutes. You’ll start to see a bit of golden color on the edges — that’s the flavor showing up to the party.
3. Time for the Creamy Sauce
Add your remaining 3 tablespoons of butter right into the pot. Once it melts, sprinkle in the flour and stir it around. It’ll look thick and pasty — that’s what you want. Let it cook for a minute (just enough to take the raw edge off the flour).
Now, here’s where you need to be patient — pour in the milk slowly, about a half cup at a time, whisking the whole time. It’s gonna look weird and lumpy at first. Keep whisking. It’ll smooth out. Once it’s all in, let the sauce simmer until it thickens slightly — like gravy that wants to nap.
Stir in the thyme, nutmeg, sage, and your salt and pepper. Taste it. Should feel like a cozy sweater on your tongue.
4. Bring It All Together
Turn off the heat. Dump in your cooked rice and 1 cup of the shredded cheese. Stir it all up until the rice is coated and cheesy.
Scoop it into your prepared dish. Spread it out and top with the rest of the cheese — don’t worry if some falls on the edge. That’s where the crispy bits happen.
5. Bake It ‘Til It Bubbles
Slide that dish into the oven and bake for 25 to 30 minutes, until the top’s golden and the sides are doing a happy little bubble dance.
Let it sit for 5 minutes after baking. I know it’s hard. But you don’t want to burn your mouth — and it sets up better that way.
Little Twists & Friendly Additions
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Got some spinach or kale? Sauté it and throw it in with the rice.
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Swap out the cheese — Gruyère is real fancy, or a little mozzarella for melt.
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Add shredded rotisserie chicken or leftover turkey — now it’s a full meal.
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No rice? Use quinoa or barley. It’s a whole new thing, but still tasty.
Leftovers? Lucky You
Pop any extras in a container and stick it in the fridge — it keeps well for 3–4 days. Reheat in the microwave or oven. You might wanna add a splash of milk when reheating to bring the creaminess back.
It also freezes — just wrap it tight. Thaw overnight in the fridge and reheat like usual.
Come Back and Tell Me How It Went
If you try this one, promise me you’ll leave a comment or shoot me a message. I love knowing how my recipes turn out in your kitchen. Did you sneak in extra cheese? Did your picky kid actually eat mushrooms for once?
Don’t be a stranger — and remember, sometimes the best meals are made from what’s already in your fridge.
Cheesy Mushroom Rice Casserole
Ingredients
- 6 tablespoons unsalted butter, divided
- 1 small onion, finely chopped
- 8 to 10 ounces mushrooms, cleaned and roughly chopped
- 3 tablespoons all-purpose flour
- 2 3/4 cups whole milk, room temperature
- 1 teaspoon dried thyme
- 3/4 teaspoon ground nutmeg
- 1/2 teaspoon dried sage
- 4 cups cooked white rice
- 1 3/4 cups grated white cheddar cheese, divided
- Kosher salt and freshly cracked black pepper, to taste
Instructions
- Preheat oven to 350°F. Grease a 9x9 casserole dish, place it on a foil-lined baking sheet, and set aside.
- In a medium saucepan, melt 3 tablespoons butter over medium heat. Add onion and cook until softened and translucent, about 8–10 minutes.
- Stir in mushrooms and cook until golden, about 4–5 minutes.
- Add remaining 3 tablespoons butter, then whisk in flour to make a roux.
- Gradually whisk in milk, 1/2 cup at a time, until incorporated and sauce is thickened.
- Stir in thyme, nutmeg, and sage. Season with salt and pepper.
- Remove from heat and fold in rice and 1 cup of cheddar cheese until combined.
- Pour mixture into the prepared casserole dish and sprinkle with remaining 3/4 cup cheese.
- Bake for 25–30 minutes, or until bubbly around the edges and golden on top. Serve warm.
Notes