Portabella Mushroom and Vidalia Onion Gratin
This Portabella Mushroom and Vidalia Onion Gratin is a spectacular way to enjoy mushrooms and sweet Vidalia onions together in the form of a casserole. It’s a magnificent side dish to serve alongside steak, pork, kabobs or chicken during grilling season. Likewise, it will fit perfectly on your holiday table too, with Prime Rib or filet. It’s a special dish for a special occasion.
Easy Portabella Mushroom and Vidalia Onion Gratin Recipe
Vidalia onions are a sweet onion grown in Vidalia Georgia. The different varieties are unusually sweet compared to other onions due to the low amount of sulfur found in the soil in which they’re grown. So beloved are these sweet onions that they were named the official State vegetable of Georgia in 1990 and rightly so, they’re a Southern delicacy worth noting. How to make Portabella Mushroom and Vidalia Onion Gratin: (Scroll down for full printable recipe.)
- Prepare Dish – Preheat the oven to 350°F. Butter the bottom and sides of a 1 1/2 quart baking dish, then set aside. (Alternately use single serving gratin dishes)
- Cook – Saute mushrooms and sliced onions in a couple of drizzles of olive olive. Cook for 10 minutes or until mushrooms are golden.
- Season – Season with salt and black pepper, adjust to taste. Add butter, minced garlic, thyme, red wine vinegar and green onions. Continue to saute over medium heat for 2 minutes just until the garlic has cooked and the butter has melted.
- Sauce – Add flour and stir until the flour has coated all of the ingredients. Increase the heat to medium high and add milk. Cook until the mixture is bubbly and has begun to thicken. Around 2-3 minutes.
- Cheese – Add shredded cheese and Italian parsley to the pot. Mix just until the cheese melts.
- Topping – In a small bowl melt remaining butter in the microwave. Toss the breadcrumbs, Parmesan and remaining Italian parsley together with the butter.
- Transfer to Dish – Pour into the buttered baking dish and sprinkle the remaining shredded Muenster cheese and breadcrumbs on top.
- Bake – Bake per the recipe until the topping is golden and the edges are bubbly.
- Let Stand – Allow the gratin to sit on the counter for 5-10 minutes before serving to allow the sauce to thicken.
How to Make the BEST Portabella Mushrooms and Vidalia Onion Gratin
This portabella mushroom and onion gratin is sprinkled with a crunchy breadcrumb topping making it an incredible way to change up your side dish menu. Filled with tasty cheesy mushrooms and Vidalia onions and a crispy crumb topping, it can be baked in one dish or you can divide it among several gratin dishes for a gorgeous presentation for individuals.
- Ingredients you’ll need to make Portabella Mushroom and Vidalia Onion Gratin:
- Kitchen tools you’ll need: 2 quart baking dish, sharp knife and cutting board, 12 inch skillet, measuring cups and spoons and cheese grater.
- When making this dish in an oven safe skillet, there’s no need to transfer to a baking dish. Simply top with crumbs and pop it into the oven to brown.
- You can prepare the mushrooms and onion mixture in advance, then top it with crumbs just before baking and serving.
- While this Portabella Mushroom And Vidalia Onion Gratin is primarily enjoyed as a side dish it’s also delightful served as a topping for baked potatoes, ladled over egg noodles or buttered rice. Try spooning this gratin over a piece of Italian seasoned grilled chicken topped with a sprinkle of cooked pancetta or bacon. It’s heavenly!
- Store this dish chilled in the refrigerator for up to 3 days.
- Reheat in single servings in the microwave or in a preheated 350°F oven to crisp the crumb topping and heat through.
More Easy Side Dish Recipes to Make
- If you love Vidalia onions too, checkout my recipe Beer Battered Onion Rings, too.
- Simply glorious Easy Mashed Potatoes.
- simple stovetop Bacon Mac and Cheese.
- Twice Baked Potatoes are a make ahead option.
- Sweet Honey Roasted Carrots.
- Treat the family to Homemade Breadsticks.
- The family always swarms a platter filled with Homemade French Fries.
- Roasted Rutabaga from Food Network.
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Helpful Kitchen Items:
Portabella Mushroom and Vidalia Onion Gratin
Ingredients
- 1 pound baby portabella mushrooms sliced
- 1 extra large vidalia onion or 2 medium sliced into small wedges
- olive oil
- 1 tsp salt
- 1/2 tsp freshly ground black pepper
- 4 Tbsp butter divided
- 3 cloves garlic minced
- 2 tsp fresh thyme
- 1 Tbsp red wine vinegar
- 3 finely chopped green onions
- 2 1/2 Tbsp all purpose flour
- 1 1/2 cups whole milk
- 2 cups shredded Muenster cheese divided
- 2 Tbsp chopped Italian parsley divided
- 1 1/2 cups fresh bread crumbs
- 2 Tbsp grated Parmesan cheese
Instructions
- Preheat the oven to 350°F. Butter the bottom and sides of a 1 1/2 quart baking dish, then set aside. (Alternately use single serving gratin dishes or an oven safe skillet.)
- In a heavy saucepan, saute mushrooms and sliced onions in a couple of drizzles of olive olive. Cook for 10 minutes or until mushrooms are golden. Season with salt and black pepper, adjust to taste.
- To the mushrooms, add 3 Tbsp butter, minced garlic, thyme, red wine vinegar and green onions.
- Continue to saute over medium heat for 2 minutes just until the garlic has cooked and the butter has melted.
- Add flour and stir until the flour has coated all of the ingredients.
- Increase the heat to medium high and add 1 1/2 cups of milk. Cook until the mixture is bubbly and has begun to thicken. Around 2-3 minutes.
- Add 1 1/2 cups of shredded cheese and 1 tablespoon of chopped Italian parsley to the pot. Mix just until the cheese melts. Remove from the heat mixing in 1 Tbsp parsley.
- In a small bowl melt remaining 1 Tbsp butter in the microwave. Toss the breadcrumbs, Parmesan and remaining Italian parsley together.
- Pour the mushrooms into the buttered baking dish and sprinkle the remaining shredded Muenster cheese and breadcrumbs on top.
- Bake for 25-30 minutes until the topping is golden and the edges are bubbly.
- Allow the gratin to sit on the counter for 5-10 minutes before serving to allow the sauce to thicken.