heat half the butter and the oil over low heat.
Add onions and cook till soft.
Add garlic and sauté till fragrant.
Add Old Bay Seasoning to brown sugar and mix together.
Add remaining butter and simmer gently until butter melts, stirring constantly.
Add broth and cook briefly until slightly thickened.
Remove from heat and serve poured over your seafood boil, or use as a dipping sauce.