How to Make It
Cut sausage in half lengthwise; cut crosswise into thin half-moon slices. Heat a large Dutch oven over medium-high. Add 1 1/2 teaspoons oil; swirl to coat. Add sausage; sauté until browned, about 3 minutes, stirring occasionally. Remove sausage from pan; set aside.
Add remaining 1 1/2 tablespoons oil to pan; swirl to coat. Add onion, celery, and carrot; sauté 5 minutes. Add stock, scraping bottom of pan to loosen browned bits. Stir in potatoes, thyme, and bay leaves. Bring to a boil; partially cover, reduce heat, and simmer until potatoes are almost tender, about 12 minutes. Stir in corn; cook 5 minutes or until potatoes are tender.
Ladle about half of soup mixture into a blender; add milk and flour. Remove center piece of blender lid (to allow steam to escape); secure lid on blender. Place a clean towel or a few layers of paper towels over opening in blender lid (to prevent splatters). Blend mixture until smooth.
Pour pureed mixture into pan. Add pepper and salt. Bring to a boil over medium heat, stirring frequently. Cook until thickened, stirring frequently, about 2 minutes. Ladle chowder into bowls; sprinkle with scallions.