Andouille Corn Chowder

Name: Andouille Corn Chowder
Ingredients: 1 tablespoon extra-virgin olive oil; 9 ounces (approximately 3 links) precooked turkey Andouille sausage, diced small; 1-1/2 cups diced yellow onion; 1/2 teaspoon kosher salt, plus a pinch; 2 tablespoons all-purpose flour; 1 large clove garlic, minced; 2-1/2 cups chicken stock; 1 medium russet potato; 1-1/2 cups whole milk or half-and-half; 3 cups corn kernels, fresh or frozen; Ground black pepper; 1 tablespoon unsalted butter to finish (optional); Chopped fresh parsley for garnish