Preheat the Oven to the Right Temperature
The first step in roasting mushrooms is preheating your oven to 375 degrees. Then, like a baking sheet with foil. We recommend that you utilize a rimmed baking sheet so that the mushrooms won't slide off of the baking sheet while you are putting the mushrooms into the oven. Tear off a sheet of aluminum foil and lay it down on the bottom of the rimmed baking sheet you are using. If you happen not to have aluminum foil, parchment paper also works.
Wash the Mushrooms at the Beginning
You have likely heard that it is generally not a good idea to wash mushrooms. However, you can actually wash mushrooms, but you should use cold water if you choose to wash mushrooms. Mushrooms only gain roughly 2% of their entire weight when you wash them.
This is too little to significantly increase the amount of time you need to cook the mushrooms. You can dry them off by spinning the mushrooms around in a salad spinner. We recommend that you first cut and then trim the mushrooms before you begin to wash them, though.
Rinse Off the Mushroom Caps
Now rinse off the mushroom caps using cold water. This helps get rid of debris or dirt that might be in the mushroom caps. You can then slice each mushroom cap into quarters. Simply throw the stems out. If you don't want to toss out the stems, you can save them for now and use them as an ingredient when you make vegetable stock.
Season the Mushrooms Properly
The next step in roasting mushrooms is to put all of the mushroom quarters from earlier into a bowl. You can then pour some extra virgin olive oil into the bowl to add some flavor. Next, season the mushrooms with some salt and pepper. Use a large spoon to gently toss the mushrooms. Toss the mushrooms until they are covered in olive oil.
Put the Mushrooms on the Baking Sheet
Place the mushroom quarters onto the baking sheet using a spoon. You should arrange them so that the mushrooms are in an even layer. Put eight to 12 fresh sprigs of rosemary or thyme on top of the mushrooms. The herbs add flavor to the mushrooms while the mushrooms are cooking.
Roast the Mushrooms in Your Oven
Put the mushrooms into your oven and roast them for 15 minutes until they get a little soft. Take out the sheet and put a bowl on the counter. Carefully drain the liquid from the mushrooms into the bowl. Continue roasting the mushrooms for an additional 30 minutes. The mushrooms should get tender, and you can expect them to shrink a bit.
Toss the Mushrooms Along With Herbs
Turn the oven off and take out the baking sheet. Get rid of the rosemary or thyme sprigs, and spoon the mushrooms into a dish so you can serve them. Get 2 tablespoons of some kind of chopped fresh herbs like chives, tarragon, or parsley and stir that in with the mushrooms. Serve the mushrooms while they are still warm. Put any leftover mushrooms into an airtight container, and they should last between three and five days.