1. Cook shrimp with heads on and unpeeled in 1 quart of water. Add 2 tbs of crab boil and medium quartered onion to water and boil for 20 minutes.
2. Remove from heat and add 3 tbs of salt, stir and let stand for 5 minutes. Drain and peel shrimp. Reserve liquid and cook the elbow macaroni in it until al dente.
3. In a large bowl, combine drained macaroni, chopped onion, celery, bacon, garlic, chopped egg whites and parsley.
4. In a separate bowl, combine mashed egg yellows with 1 tsp salt, 1 tsp cayenne, 1 tsp crab boil, mayonnaise and bacon fat until well blended.
5. Add to macaroni and mix well. Sprinkle paprika on top.