Spinach, Mushroom and Brie Grilled Cheese Sandwiches

Ingredients

• 1 tbsp (15 mL) extra-virgin olive oil
• ½ lb (250 g) cremini mushrooms, trimmed and sliced
• 10 oz (300 g) baby spinach, rinsed and dried
• kosher salt and freshly ground black pepper
• 8 slices multigrain or whole wheat bread
• 6 oz (175 g) brie cheese, crust on or off, thinly sliced
• 2 tbsp (25 mL) soft butter—optional