2 tablespoons unsalted butter |
1 medium leek, green parts only, chopped |
4 cups chicken stock, or canned low-sodium broth |
1 medium potato, peeled and diced |
2 cups half-and-half |
3/4 cup freshly grated provolone |
3/4 cup freshly grated parmesan |
3/4 cup freshly grated mozzarella |
3/4 cup freshly grated cheddar |
freshly chopped tarragon leaves, for garnish |