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Cheesy Mushroom Casserole: Easy Low-Carb, Gluten-Free Side Dish

A warm baked dish of Cheesy Mushroom Casserole with rich golden topping, perfect for What To Make With Lots Of Mushrooms.
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This Cheesy Mushroom Casserole combines sautéed mushrooms, onions, garlic, thyme, and melted Gruyere into a rich, savory side dish that is naturally low-carb and gluten-free. It is ready fast, tastes elegant, and works for both everyday dinners and special occasions.

Ingredients

Scale
  • 1/4 cup olive oil, plus more for greasing the dish
  • 32 ounces baby bella or crimini mushrooms, sliced
  • 1 cup chopped onions
  • 2 teaspoons Diamond Crystal kosher salt, or 1 teaspoon of another salt such as Morton kosher salt
  • 1 tablespoon fresh garlic, minced
  • 1/2 teaspoon black pepper
  • 1/2 teaspoon dried thyme
  • 1 cup shredded Gruyere cheese
  • 1 teaspoon dried parsley, for garnish

Instructions

  1. Heat the oven to 400°F. Lightly coat a 2-quart baking dish with olive oil so the casserole releases easily after baking. Preparing the dish first helps Cheesy Mushroom Casserole move quickly once the mushrooms are ready.
  2. Set a large, deep skillet over medium-high heat and pour in the olive oil. Let it warm up for a moment, then add the sliced mushrooms, chopped onions, and kosher salt. Stir everything together so the vegetables start cooking evenly. The salt will help pull moisture out of the mushrooms, which is exactly what Cheesy Mushroom Casserole needs.
  3. Continue cooking the mushrooms and onions, stirring now and then, until the mushrooms have given off their liquid and most of that liquid has evaporated. This should take about 10 minutes, though the exact time can vary depending on your pan and the heat. Do not rush this step. Drying out the mushrooms first keeps Cheesy Mushroom Casserole from becoming watery.
  4. Once the pan looks mostly dry, add the minced garlic, black pepper, and dried thyme. Stir everything together and cook for about 1 more minute, just until the garlic smells fragrant and the herbs bloom in the hot pan. At this point the mushroom mixture for Cheesy Mushroom Casserole should smell rich and savory.
  5. Remove the skillet from the heat and transfer the mushroom mixture to the prepared baking dish. Spread it out into an even layer so the cheese melts evenly across the top of Cheesy Mushroom Casserole.
  6. Sprinkle the shredded Gruyere evenly over the mushrooms. Try to cover the whole surface so every serving gets a cheesy top layer. This is the part that turns the dish from sautéed vegetables into Cheesy Mushroom Casserole.
  7. Bake the casserole for about 15 minutes, or until it is hot, bubbling, and the cheese has melted completely. Once it comes out of the oven, sprinkle the dried parsley over the top for a little color and a fresh finish. Serve Cheesy Mushroom Casserole immediately while it is hot and melty.

Notes

  • If your baking dish is broiler-safe, you can skip the bake and broil the casserole for 2 to 3 minutes instead, keeping it in the middle of the oven so the cheese melts without burning.
  • Seasoning amounts are flexible, especially the salt. Taste and adjust as needed.
  • Mushrooms shrink a lot as they cook, so 32 ounces fits nicely into a 2-quart casserole dish after sautéing.
  • Baby bella or crimini mushrooms usually look a little more polished than white mushrooms, which is why they are often the best choice for Cheesy Mushroom Casserole.
  • Store leftovers in an airtight container in the fridge for up to 4 days. Reheat gently in the microwave at 50% power.

Nutrition

Find it online: https://irmacooks.com/cheesy-mushroom-casserole/