Lightly spray the inside of the slow cooker with cooking spray. Add the frozen hash browns, shredded cheddar, onion, and garlic, then stir to combine.

In a separate mixing bowl, whisk together the cream of chicken soup, sour cream, half of the melted butter, salt, and black pepper until smooth.

Pour the soup mixture over the potatoes and gently fold everything together until evenly coated. Spread the mixture into an even layer.

Cover and cook on LOW for 5–6 hours or HIGH for 3–4 hours, until the potatoes are tender and the cheese is melted.

Once the potatoes are cooked, switch the slow cooker to the WARM setting while you prepare the topping.

Heat a skillet over medium heat and melt the remaining butter. Stir in the crushed cornflakes and cook for about 3 minutes, stirring often, until golden and crisp.

Sprinkle the toasted cornflakes over the potatoes just before serving.