Keto Sausage Cabbage Casserole with "Fettuccini" Alfredo

Ingredients

• 1 medium head of cabbage
• 1 medium yellow onion
• 4 garlic cloves, minced
• 1/4 cup salted butter (half a stick) + 2 tablespoons, divided
• 2 - 8 oz. blocks full-fat cream cheese
• 1/2 cup full-fat sour cream
• 1/4 cup heavy whipping cream
• 1/2 teaspoon salt
• 1/2 teaspoon pepper
• 1 teaspoon garlic powder
• Lemon juice from 1 large lemon
• 1 cup parmesan cheese, shaved or shredded
• 1 pound Italian sausage links
• 2 tablespoons parsley, chopped, to garnish