Prep the potatoes. Peel and dice the russets into 1/2-inch cubes. Smaller pieces cook faster and mash more easily.
Load the slow cooker. Add potatoes, onion, garlic, broth, paprika, 1 teaspoon salt, and 1/2 teaspoon pepper. Dot with butter.
Cook low and slow. Cover and cook on Low for 6–8 hours, or on High for 3–4 hours, until the potatoes are very tender.
Crisp the bacon. While the soup cooks, fry the bacon until crisp.
Drain and crumble. Set aside for topping and stirring in.
Thicken (optional). For a thicker soup, whisk flour with the milk until smooth. Stir the slurry into the slow cooker.
Cook 20–30 more minutes on High to thicken.
Mash to your liking. Use a potato masher to mash some of the potatoes right in the pot. Leave some chunks for texture, or blend briefly with an immersion blender for extra creaminess.
Finish creamy. Stir in sour cream and 1 cup of the shredded cheddar. Taste and adjust salt and pepper.
If you like it richer, add a splash more milk or a few cubes of cream cheese.
Serve and top. Ladle into bowls. Top with bacon, extra cheddar, and green onions. Add hot sauce if you want a little kick.