Slow Cooker Cream of Mushroom Soup

Name: Slow Cooker Cream of Mushroom Soup
Ingredients: 1 1/2 pounds cremini mushrooms, sliced 1/4-inch thick; 4 tablespoons (1/2 stick) unsalted butter, melted; 3/4 teaspoon kosher salt; 1 medium yellow onion, diced; 2 cloves garlic, minced; 2 cups low-sodium vegetable broth; 2 tablespoons dry sherry; 1/4 ounce dried porcini mushrooms, cut into 1/4-inch pieces; 1/2 teaspoon freshly ground black pepper; 1/2 teaspoon dried thyme; 1/4 teaspoon dried tarragon; 1/2 cup heavy cream, plus extra for serving; 2 teaspoons freshly squeezed lemon juice; Chopped fresh thyme or tarragon leaves, for serving