Mushrooms and Onions Recipe

Ingredients

• 454 g (1 lb)mushrooms, cleaned and stems trimmed flush with the caps (cremini or white button)
• 227 g (8 oz)pearl onions, defrosted if frozen
• 30 ml (2 tbsp)good-quality olive oil
• To tastesea salt and ground black pepper
• 71 g (5 tbsp)unsalted butter, cut into cubes
• 80 ml (⅓ cup)dry white wine
• 2–3 clovesgarlic, minced
• 10 ml (2 tsp) eachfresh thyme and fresh oregano, chopped, plus extra sprigs for roasting
• Optionalfresh parsley and lemon wedges, for garnish

Instructions

1. 1

   Preheat the oven

   Set an oven rack in the middle position and heat the oven to 220°C (425°F).

2. 2

   Season the vegetables

   Put the mushrooms and onions on a large rimmed baking dish. Drizzle with the olive oil, season with a pinch of salt and pepper, then arrange in one well-spaced layer with the mushrooms stem-side down. Add 4 sprigs of fresh thyme and 2 sprigs of rosemary on top, as directed in the method.

3. 3

   Roast briefly

   Roast the mushrooms and onions for 15 minutes, or until they begin to brown lightly.

4. 4

   Make garlic butter

   Meanwhile, combine the butter, wine, garlic, chopped thyme and oregano in a large microwave-safe liquid measuring cup. Season with ¼ teaspoon salt and ⅛ teaspoon pepper. Microwave at 50% power for 1 minute, stir, then heat at 50% power for another 1½ minutes in 30-second intervals.

5. 5

   Add the sauce

   Take the baking dish out of the oven and drizzle the butter sauce evenly over the vegetables. Toss or stir gently to coat.

6. 6

   Finish roasting

   Return the dish to the oven for 5–10 minutes, until the mushrooms are browned and tender. Taste and adjust the salt and pepper.

7. 7

   Garnish and serve

   Transfer the mushrooms and onions to a serving dish, then spoon any butter sauce left in the baking dish over them. Add fresh herbs and lemon if using, and serve straight away.

What are mushrooms and onions?

This American-style side pairs roasted mushrooms with pearl onions and a buttery herb sauce. Roasting brings out savoury, sweet notes in both vegetables, while white wine and garlic give the butter a bright, aromatic finish.

The method keeps the vegetables in a single layer and adds the sauce partway through. That gives the mushrooms time to brown before they are coated.

Nutrition and macros by portion

The nutrition label shows one serving as written: 169 calories, 3g protein, 7g carbs, 14g fat.

The mushrooms and onions provide most of the carbohydrates, while the butter and olive oil supply most of the fat. The mushrooms contribute a little protein, but this side is not a substantial protein source; pair it with chicken, steak, beans or another protein-rich main and add a green vegetable to round out the plate.

Choose the mushrooms and onions

Mushrooms: Cremini have a deeper flavour, while white button mushrooms are milder; either works here. Trim the stems flush with the caps so the mushrooms sit evenly on the tray.

Pearl onions: Frozen onions are convenient, but defrost them before roasting as the recipe directs. Pat away excess moisture if they are wet, so the vegetables roast rather than steam.

Make the garlic butter

Gentle heat: Microwaving the butter mixture at half power helps it melt without aggressively bubbling. Stir between intervals so the butter, wine, garlic and herbs combine evenly.

Seasoning: The sauce has salt and pepper, and the vegetables are seasoned separately. Taste at the end and adjust carefully, since the butter sauce gathers in the baking dish.

Look for browning and tenderness

First roast: After 15 minutes, the vegetables should be starting to colour. The mushrooms should remain intact and should not be crowded together.

Final roast: After the sauce is added, roast for another 5–10 minutes. The mushrooms are ready when browned and tender, and the onions are hot through.

Keep the tray uncrowded

Spacing: Arrange the mushrooms and onions in one well-spaced layer, with the mushrooms stem-side down. If they are packed tightly, moisture can collect and slow browning.

Sauce timing: Add the garlic butter only after the first roast. This lets the vegetables begin to colour before the butter and wine coat them.

Serve alongside a main

Pairings: Spoon the vegetables and their sauce beside steak or chicken, or serve them over pasta. A squeeze of lemon and a little parsley can balance the richness.

For a fuller plate, add a plain grain or another vegetable alongside them. Bring the remaining sauce from the tray to the table for spooning over the mushrooms and onions.

Recipe notes & tips

• Dry the mushrooms after cleaning so excess water does not hinder browning.
• Use a large rimmed baking dish and leave space between the vegetables.
• Choose a dry white wine you would be happy to drink.
• Microwave the butter mixture in short intervals and stir it well between rounds.
• Taste the vegetables after the final roast before adding more salt or pepper.
• Add parsley and lemon just before serving for a fresh finish.

Variations

• Use cremini mushrooms: Choose them for a deeper, earthier flavour.
• Try white button mushrooms: Use them for a milder result.
• Add lemon: Squeeze a wedge over the vegetables just before serving.
• Use parsley: Scatter chopped fresh parsley over the dish as a garnish.
• Change the herbs: Use the listed thyme and oregano to give the butter sauce an aromatic finish.

Common mistakes to avoid

• Crowding the dish: The vegetables can steam instead of brown; spread them in a single layer.
• Skipping the first roast: Add the butter sauce only after the initial 15 minutes so the vegetables can start to colour.
• Overheating the butter: Use 50% microwave power and stir between intervals.
• Leaving wet vegetables: Pat off excess moisture before roasting to help them brown.
• Relying only on the initial seasoning: Taste after roasting and adjust salt and pepper before serving.

How to store

Refrigerate leftovers in an airtight container for up to 3 days. Reheat gently in a covered pan over low heat or in the microwave until hot; the mushrooms will be softer after storage.

Frequently asked questions