Cook the Bacon: In a large pot over medium heat, cook 1/2 lb chopped bacon until crisp, about 5-7 minutes. Remove bacon with a slotted spoon, leaving grease in the pot.
Sauté the Vegetables: Add 1 diced onion, 1/2 diced bell pepper, and 2 diced celery stalks to the bacon grease. Sauté for 5-7 minutes until softened. Add 4 minced garlic cloves and cook for 1 minute until fragrant.
Make the Roux: Deglaze the pot with 1/4 cup sherry, scraping up browned bits. Add 8 tbsp butter and let it melt. Sprinkle in 1/2 cup flour and stir for 2-3 minutes until thick and clumpy.
Add Liquids: Gradually whisk in 4 cups shrimp stock, 1/2 cup at a time, until smooth and no lumps remain. Stir in 1 1/2 cups water. Bring to a simmer.
Simmer the Base: Add half of the chopped parsley and half of the sliced green onions. Simmer uncovered for 30 minutes, stirring occasionally, to develop flavors.
Finish the Soup: Stir in 1 1/2 lbs shrimp, 2–3 cups corn kernels, 2 cups warmed heavy cream, 1 tbsp Cajun seasoning, and the remaining parsley and green onions. Simmer for 5-7 minutes until shrimp are pink and opaque. Taste and adjust with black pepper or additional Cajun seasoning.
Serve: Ladle into bowls, garnish with reserved bacon, extra green onions, or parsley, and serve hot with crusty bread for a perfect dinner idea.