Butternut Squash and Cauliflower Chowder

Name: Butternut Squash and Cauliflower Chowder
Ingredients: 2 Tbs. unsalted butter; 1 medium leek, halved lengthwise, rinsed, then thinly sliced (1 1/3 cups); 1 3/4 lb. butternut squash, peeled, seeded, and diced into 1/2-inch cubes (4 cups); 1 small head cauliflower florets, chopped or broken into bite-size pieces (41/2 cups); 2 Tbs. all-purpose flour; 2 1/2 cups low-sodium vegetable broth; 1 1/2 cups low-fat milk; 1 bay leaf; 2 sprigs fresh thyme; 2/3 cup frozen corn; 2 Tbs. grated lemon zest