900 grams mixed mushrooms (king oyster, shiitake, oyster and cremini, sliced or torn)
2 cloves garlic, finely chopped
2 sprigs rosemary
1/4 cup (60 milliliters) dry white wine
3 tablespoons (45 milliliters) olive oil
2 tablespoons (30 milliliters) balsamic vinegar
1 tablespoon (15 grams) grainy Dijon mustard, plus more for serving
Freshly ground black pepper
1/2 cup (125 milliliters) mayonnaise
2 tablespoons (30 grams) prepared horseradish
3 tablespoons (5 grams) finely chopped tarragon
2 tablespoons (8 grams) finely chopped chives
8 slices sourdough bread, lightly toasted or grilled and rubbed with garlic
2 handfuls arugula
Optional: 125 grams brie cheese, thinly sliced
Preheat oven to 450°F (232°C).
Place mushrooms onto a large rimmed baking sheet with garlic and rosemary. If mushrooms are crowded, use two smaller sheets.
Whisk together wine, olive oil, vinegar and mustard in a small bowl. Season with salt and pepper. Pour over mushrooms and toss to combine. Spread mushrooms into a single layer. Roast until golden and beginning to become crisp, about 20 to 25 minutes, stirring halfway through.
Mix together mayonnaise, horseradish, tarragon and chives in a small bowl. Season with pepper.
To assemble the sandwiches: Spread mixture from step 4 onto one side of four slices of toasted or grilled bread. Spread Dijon onto one side of remaining four slices of bread. Layer with arugula, warm mushrooms and brie cheese, if using.