Step 1

Adjust oven rack to center position and preheat the oven to 400°F.

Step 2

In a large bowl, add the garlic, rosemary, red wine vinegar, mustard, red pepper flakes, 1/2 teaspoon salt, and 1/2 teaspoon pepper and whisk until well combined. Slowly drizzle in the olive oil, while constantly whisking, and mix until the dressing thickens and emulsifies. Add the mushrooms to the bowl and toss until all the mushrooms are coated in the dressing.

Step 3

Pour the dressing and the mushrooms into a large baking dish and arrange the mushrooms in a single layer. Place the mushrooms in the oven and roast for 15 minutes. Using a wooden spoon, stir the mushrooms, then continue roasting until the mushrooms are tender, about 10 minutes longer.

Step 4

Allow the mushrooms to cool slightly. Transfer the mushrooms to a large serving dish, then stir in the lemon juice. Season to taste with more salt and pepper, and garnish with chopped parsley. Serve the mushrooms warm, or at room temperature, with crusty bread for dipping into the extra dressing.