In a large bowl, add eggs and gently whisk. Then add dry mustard, garlic powder, sea salt, pepper, and milk. Gently whisk until ingredients are well incorporated, without over-whisking.
Coat slow cooker with non-stick spray. We are now going to alternate layers of ingredients: Use first portion of divided hash browns and spread across bottom. Season with a little sea salt and pepper. Then add a layer of the divided cheddar cheese.
Add diced sausage. Add the remaining hash browns, season with sea salt and pepper, pour egg mixture over top, and finish with remaining cheddar cheese.
Cover and cook on low for approximately 7 hours or on high for 3 ½ -4 hours.