In a large saucepan over medium heat, melt the butter. Add the chopped onion and sauté until translucent, about 5 minutes.
Add the minced garlic and cook for an additional 2 minutes, stirring frequently to prevent burning.
Stir in the Old Bay seasoning, smoked paprika, lemon pepper seasoning, cayenne pepper, red pepper flakes, and brown sugar. Cook for 1-2 minutes until the spices are fragrant.
Pour in the Worcestershire sauce, hot sauce, seafood or chicken broth, and lemon juice. Stir to combine and bring the mixture to a simmer.
Reduce the heat to low and let the sauce simmer for 10-15 minutes, allowing the flavors to meld together. Stir occasionally.
Taste and adjust seasoning with salt and freshly ground black pepper as needed.
Remove from heat and garnish with chopped fresh parsley.
Serve the sauce warm alongside your favorite seafood boil ingredients, such as shrimp, crab legs, corn on the cob, and potatoes.