Start by preheating your oven to 220°C (450°F), or 200°C if you have a fan/convection oven. While that's heating, grab a large baking tray and have it ready. You want your oven nice and hot so those mushrooms will develop golden, caramelized edges. This temperature is crucial—it's hot enough to drive off moisture but not so hot that the outside burns before the inside cooks.

Clean your mushrooms by wiping them gently with a damp paper towel. I know there's debate about rinsing mushrooms, but honestly, they can handle a quick rinse under cool water. Just pat them dry immediately. Leave smaller mushrooms whole, but if you're using large portobellos, cut them in half or quarters so they cook evenly. You want pieces roughly similar in size so everything finishes at the same time.

In a large mixing bowl, combine your melted butter, olive oil, minced garlic, salt, and pepper. Use a rubber spatula to mix these together until the garlic is evenly distributed throughout the fat. This might seem like an extra step, but coating your mushrooms evenly matters. You want every piece to get some garlic and seasonings.

Add your prepared mushrooms to the butter mixture and toss gently but thoroughly using that rubber spatula. Make sure every mushroom surface is coated with the buttery mixture. This is where the flavor comes from—the butter and garlic will help create those beautiful caramelized edges while keeping everything moist inside.

Pour the mushrooms and all their buttery coating onto your baking tray, spreading them in a single layer. This is important—don't pile them on top of each other. They need space for the hot air to circulate. If they're crowded, they'll steam instead of roast, and steamed mushrooms are watery mushrooms. Nobody wants that.

Pop the tray into your preheated oven and roast for exactly 25 minutes. This is key—don't toss or turn them during cooking. I know it's tempting to peek and stir, but resist that urge. The undisturbed heat allows the flat sides to make contact with the hot tray, which creates those gorgeous caramelized spots. After 25 minutes, they should be golden brown and tender, with slightly shrunken edges.

Remove the tray from the oven and immediately push the mushrooms together onto one side of the tray. This helps keep them warm and makes them easier to handle. Drizzle everything with the fresh lemon juice and sprinkle the thyme leaves over top. Toss gently to distribute, taste, and adjust seasoning if needed. The bright acidity from lemon cuts through the richness beautifully and wakes up all those savory flavors. Serve immediately while they're still warm and the edges are at their crispest.