To a large pot over medium-high heat, add oil. Once hot, add andouille and heat for about 3-5 minutes on each side, or until brown and slightly crispy on the edges.
Transfer the andouille to a plate and tent to keep warm. To the same pot, add the onions and cook for 3-5 minutes or until softened. Add garlic. Cook for 1 more minute.
Whisk in flour and continue cooking, stirring constantly, for 1 more minute. Slowly drizzle in chicken broth and milk. Whisk until no flour lumps remain.
Add potatoes, cover, and simmer for 15-18 minutes, or until potatoes are fork-tender.
Add creamed corn, sweet corn, salt, pepper, and crushed red pepper. Stir to combine.
Carefully transfer ½ of the soup to a blender and blend until smooth (be careful, the liquid will be hot).
Return the blended soup to the pot. Add the andouille. Stir to combine and cook for 3-5 more minutes or until heated through.
Serve hot, garnished with green onions.