1.Fill up a large pot with water over medium-high heat. Add old bay seasoning, 8 smashed garlic cloves, and lemon. Bring it to a boil.
2.Add corn and baby potatoes into the water. Boil for about 10 minutes. Add sausage and onions. Cover with a lid and boil for an additional 5 minutes.
3.Gently stir in crawfish. Boil for 5-6 minutes or until the crawfish turns into bright red color. Season with 1 tablespoon salt and 1 teaspoon pepper to taste. (If you crawfish is pre-cooked, you'll only need 3-4 minutes; if yours is frozen, add 2-3 more minutes.)
4.Strain the mixture into a large serving platter. Sprinkle with parsley.
5.In a small pan heat butter and add 4 minced garlic. Cook until fragrant and add a dash of salt and pepper. Transfer to a small bowl. Serve immediately with butter and bowls of seafood boil broth.