Mushroom Toasts - Fresh-Pressed Olive Oil

Ingredients

• 1 small onion, peeled and quartered
• 4 garlic cloves, peeled, one halved
• 4 tablespoons extra virgin olive oil, plus more for drizzling
• 12 ounces baby bella (cremini) mushrooms, thinly sliced
• 2 tablespoons red wine or sherry vinegar
• 1/2 teaspoon coarse sea salt, or to taste
• 1/2 teaspoon freshly ground black pepper, or to taste
• 2 tablespoons half-and-half or light cream
• 1 tablespoon chopped flat-leaf parsley
• 4 slices of crusty bread, 1/2 inch thick