Cream of Mushroom Soup

Name: Cream of Mushroom Soup
Ingredients: 4 tablespoons extra virgin olive oil; 4 tablespoons butter; 2 pounds ( 900 g ) cremini (or button) mushrooms, cleaned, roughly chopped or sliced 1/8-inch thick; Small handful shiitake mushrooms , chopped; 3/4 cup minced shallots (6 ounces, 170 g ); 3 cloves garlic, minced (3 teaspoons); 1 teaspoon kosher salt; 3/4 teaspoon dried tarragon; 4 cups ( 1 liter ) chicken stock (or vegetable stock for vegetarian option); 1/2 cup ( 120 ml ) heavy cream; 1/2 teaspoon freshly ground black pepper (more or less to taste)