Sautéed Spinach, Mushrooms, and Caramelized Onions

This sautéed spinach, mushrooms, and caramelized onions dish is a rich and flavorful side that pairs perfectly with pasta, grilled meats, or seafood. The creamy sauce with Parmesan cheese and balsamic vinegar adds depth, making it a versatile and satisfying accompaniment.

Why You’ll Love This Recipe

I love this recipe because it’s packed with layers of flavor—from the sweetness of caramelized onions to the earthiness of mushrooms and the freshness of spinach. The creamy sauce ties everything together beautifully without being too heavy. It’s also flexible; I can make it lighter by skipping the cream or Parmesan, or use it as a hearty side or a topping for pasta or grilled dishes.

Ingredients

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

Caramelized Onions

• 1 tablespoon olive oil
• 3 large yellow onions, sliced
• ¼ teaspoon salt
• 1 tablespoon balsamic vinegar

Other Ingredients

• 1 tablespoon olive oil
• 10 oz mushrooms, sliced (I usually use button mushrooms)
• 6 oz fresh spinach
• 1 cup half-and-half
• 1 cup shredded Parmesan cheese
• ¼ teaspoon salt

Directions

How I caramelize the onions:

I heat 1 tablespoon of olive oil in a large skillet over medium-high heat. I add the sliced onions and cook them on high, stirring constantly for about 10 minutes until they start to brown but don’t burn.

Then, I reduce the heat to medium and continue cooking the onions for another 10 minutes, stirring as they deepen in color. I add a pinch of salt here to help with caramelization.

I keep cooking them on medium-low heat for a final 10 minutes, stirring occasionally to prevent sticking or burning, until they become rich and golden brown.

Once done, I remove the skillet from heat and add a splash of balsamic vinegar to deglaze the pan. I stir the onions, scraping up any flavorful bits from the bottom, then transfer the caramelized onions to a plate.

How I cook the mushrooms and spinach:

In the same skillet, I heat another tablespoon of olive oil over medium heat. I add the sliced mushrooms, sprinkle a pinch of salt, and cook for about 5 minutes until they soften, stirring occasionally.

Next, I add the fresh spinach and stir gently on low heat until it just starts to wilt.

Making the creamy sauce:

I pour in the half-and-half and bring the mixture to a quick boil, then reduce the heat to a simmer. I add about ⅔ cup of shredded Parmesan cheese and ¼ teaspoon salt, stirring continuously until the cheese melts and the sauce thickens.

Finally, I add the caramelized onions back into the skillet and mix everything well. If the sauce feels too thick, I thin it out with a little more half-and-half. If it’s too thin, I stir in a bit more Parmesan while simmering.

Servings and Timing

This recipe serves 4 people and takes about 40 minutes total—10 minutes to prep and 30 minutes to cook the onions and prepare the dish.

Variations

Sometimes I substitute half-and-half with a mix of ½ cup heavy cream and ½ cup milk for a slightly richer sauce. I can omit the Parmesan and cream to make it lighter or skip the onions if I’m short on time, simply sautéing them instead of caramelizing. For extra flavor, I occasionally add garlic or fresh herbs like thyme or parsley.

Storage/Reheating

I keep leftovers in an airtight container in the refrigerator for up to 3 days. When reheating, I warm the dish gently on the stovetop, adding a splash of half-and-half or milk to keep the sauce creamy and smooth.

FAQs

Can I make this dish vegan?

Yes, I swap the half-and-half and Parmesan for plant-based alternatives like coconut cream and vegan cheese or nutritional yeast.

Can I caramelize onions faster?

I usually take my time for the best flavor, but you can cook onions on medium-high heat while stirring constantly for about 15 minutes to speed it up, though the flavor won’t be as deep.

What mushrooms work best?

Button mushrooms are my go-to, but cremini or baby bella mushrooms work beautifully as well.

Can I use frozen spinach?

I prefer fresh spinach for the best texture, but you can use frozen spinach if you thaw and drain it well before adding.

How do I make the sauce thicker?

I add more Parmesan cheese gradually while simmering to thicken the sauce to my liking.

Conclusion

This sautéed spinach, mushrooms, and caramelized onions dish is one of my favorite side dishes because it’s full of flavor, creamy without being heavy, and versatile enough to complement a variety of main courses. It’s perfect when I want something comforting yet elegant, and I find myself making it often for weeknight dinners or holiday meals alike.

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