Add all of the ingredients to a food processor or blender and combine until smooth. Refrigerate until serving.
Can be made 24 hours in advance.
Prepare Crabs:
One hour before cooking, place soft shell crabs in a bowl and pour buttermilk or milk over them. Cover and refrigerate.
In shallow bowl, stir egg with a fork.
In a another shall bowl, stir flour, cornmeal and Old Bay.
Heat large frying pan over medium-high heat. Add oil. Once hot, remove each crab from the milk mixture, dip into egg and then into flour-cornmeal mixture. Place in frying pan. Cook 4 to 5 minutes per side until golden. Transfer to a paper towel-lined plate. Depending on the size of your pan, you may need to do this in two batches. Add extra oil as needed.