French Onion Potatoes with Crispy Onions (Creamy, Cheesy, Crunchy)

Ingredients

• 32 oz (900 g) frozen cubed hash browns, fully thawed
• 1/4 cup (57 g) unsalted butter, melted
• 2 cups (225 g) sharp cheddar cheese, freshly shredded
• 1 1/2 cups (360 g) sour cream
• 1/4 cup (57 g) unsalted butter
• 1 small yellow onion, finely diced
• 2 cloves garlic, minced
• 1/4 cup (31 g) all-purpose flour
• 1 teaspoon kosher salt
• 1/2 teaspoon black pepper
• 1/2 teaspoon dry mustard
• 1/4 teaspoon cayenne pepper, optional
• 1/2 cup (120 ml) vegetable broth
• 1/2 cup (120 ml) whole milk
• 2 large yellow onions, very thinly sliced and separated
• 3-4 cups (720-960 ml) vegetable oil, for frying
• 1/2 teaspoon kosher salt, plus more to taste