Cheesy Hash Brown Casserole

Name: Cheesy Hash Brown Casserole
Ingredients: 1 tablespoon olive oil; 1 pound uncooked mild Italian sausage, casings removed; 1 medium yellow onion, diced; 1 red bell pepper, stemmed, seeds removed, and diced; 3/4 teaspoon kosher salt, divided; 20 ounces frozen shredded hash brown potatoes, kept frozen; 10 large eggs (I used Eggland's Best); 1 cup sour cream; 1 cup milk (whole or 2%); 2 tablespoons Dijon mustard; 6 ounces (1 1/2 cups) shredded sharp cheddar cheese (I used Cabot Sharp Cheddar); 1/2 teaspoon freshly ground black pepper