Name: Caramelized Onion Sauce with Sautéed Spinach and Mushrooms
Prep time: 10 min
Cook time: 35 min
Total time: 45 min
Cuisine: American
Ingredients: 2 tbsp olive oil or butter; 2 large yellow onions, thinly sliced; 1/2 tsp salt; 1 tsp sugar (optional, to help caramelize); 8 oz mushrooms (cremini or button), sliced; 2 cloves garlic, minced; 4 cups baby spinach; 1/4 tsp black pepper; 1/4 tsp thyme (optional); 1/4 cup vegetable or chicken broth (for deglazing); 1–2 tbsp heavy cream or plant-based alternative (optional for creaminess); Grated Parmesan (optional for serving)

Why You’ll Love This Recipe

I love this recipe because it feels fancy but is actually very simple to make. The caramelized onions add a deep, almost jammy sweetness, while the mushrooms give it a hearty bite and the spinach brings freshness and color. It’s versatile enough to serve over pasta, grains, mashed potatoes, or even grilled chicken or steak if I want to bulk it up. And that sauce? Pure magic.

Ingredients

(Here’s a tip: Check out the full list of ingredients and measurements in the recipe card below.)

Yellow or sweet onions (thinly sliced)
Olive oil or butter (for caramelizing)
Garlic (minced)
Baby bella or cremini mushrooms (sliced)
Fresh spinach (chopped)
Vegetable broth or white wine (for deglazing)
Heavy cream or half-and-half (optional, for a richer sauce)
Salt
Black pepper
Fresh thyme or parsley (optional, for garnish)
Balsamic vinegar (optional, for depth and brightness)

Directions

I start by heating olive oil or butter in a skillet over medium-low heat and add the sliced onions. I cook them slowly, stirring often, for about 25–30 minutes until they’re deeply golden and caramelized.
Once the onions are ready, I add the garlic and cook for another minute until fragrant.
I increase the heat to medium and stir in the mushrooms. I let them cook down for 6–8 minutes until browned and their moisture has evaporated.
I deglaze the pan with a splash of vegetable broth or white wine, scraping up any bits from the bottom.
I add the spinach and stir until wilted, about 1–2 minutes.
For a richer sauce, I stir in a splash of cream or half-and-half and let it simmer for a few minutes to thicken. I season everything with salt, pepper, and a drizzle of balsamic vinegar if I want extra depth.
I serve it warm, topped with fresh herbs if I have them.

Servings and timing

This recipe serves 3 to 4 people as a side, or 2 to 3 as a main over pasta or grains. It takes about 10 minutes to prep and 35 minutes to cook, so I have it ready in around 45 minutes.

Variations

Sometimes I add cooked lentils or white beans to make it a heartier vegetarian main. I’ve also tossed it with cooked pasta or spooned it over polenta. For a dairy-free version, I skip the cream and rely on the richness of the caramelized onions. When I want extra protein, I add grilled chicken, tofu, or a poached egg on top.

Storage/Reheating

Leftovers keep well in the fridge for up to 3 days. I store them in an airtight container and reheat in a skillet over medium heat with a splash of broth or water. It’s not ideal for freezing because the spinach can get mushy, but it’s fine for short-term storage.

FAQs

How do I caramelize onions properly?

I cook them low and slow in oil or butter, stirring often. It takes about 25–30 minutes to get that deep golden color and sweet flavor—totally worth the time.

What kind of mushrooms work best?

I use baby bella or cremini for their meaty texture and earthy flavor, but button mushrooms or sliced portobellos work well too.

Can I make this ahead of time?

Yes, I often make the caramelized onions in advance and store them in the fridge. Then I just sauté the mushrooms and spinach when I’m ready to serve.

Do I need cream in the sauce?

Not at all. The sauce is flavorful without it, but I add cream or half-and-half when I want something richer and more comforting.

What’s the best way to serve this?

I love it over pasta, mashed potatoes, quinoa, or even crusty toast. It also makes a fantastic topping for steak, chicken, or a baked sweet potato.

Conclusion

Caramelized Onion Sauce with Sautéed Spinach and Mushrooms is a cozy, elegant dish that turns simple ingredients into something truly special. I love the mix of sweet onions, earthy mushrooms, and fresh greens—all tied together in a savory, spoon-worthy sauce. Whether I’m making a quick weeknight dinner or dressing up leftovers, this recipe always delivers comfort and flavor.