Make the dressing. Mix the cream cheese, 4 ounces of shredded cheddar cheese, mayonnaise, sour cream, Old Bay, Worcestershire sauce, lemon juice, and ground mustard in a large bowl until well combined.
Fold in the lump crab meat. Carefully fold in the lump crab meat into the cream cheese mixture. You’ll want to avoid breaking the clumps as much as possible.
Spread the dip into a baking dish and bake. Top with the remaining shredded cheddar cheese and a sprinkle of Old Bay seasoning. Place the dish in the preheated oven and bake for 25 to 30 minutes or until the dip is hot and bubbling.