Mushroom Toasts with Watercress and Chives

Name: Mushroom Toasts with Watercress and Chives
Ingredients: 6 tablespoons olive oil, divided, plus more for drizzling; 4 ¾-inch-thick slices country-style bread; 1 garlic clove; Kosher salt; 2 tablespoons unsalted butter; 12 ounces mixed mushrooms, such as morels, chanterelles, crimini, and/or maitake, coarsely chopped; 1 medium shallot, finely chopped; 1 tablespoon dry white wine; 1 cup crème fraîche or sour cream; 1 teaspoon chopped thyme; ½ teaspoon finely grated lemon zest; Freshly ground black pepper; 1 cup (loosely packed) trimmed watercress, torn; 2 teaspoons fresh lemon juice; 1 tablespoon finely chopped chives