Preheat oven to 300°F. Line a baking sheet with wax paper.
Combine crabmeat, scallions, bell pepper, parsley, dill, and 3⁄4 cup cracker crumbs in a large bowl and mix to blend. Put the remaining crumbs in a shallow bowl and set aside.
In a third bowl, combine the egg, mayonnaise, seafood seasoning, mustard, and Worcestershire sauce and whisk to blend. Add the egg mixture to the crab mixture and stir until the ingredients cohere.
Shape the crabmeat mixture: For “silver dollar”–size cakes, use 1 heaping tablespoon of the mixture; for larger cakes, use about 1⁄3 cup. Form crab balls. Roll each ball in the cracker crumbs. Flatten each ball into a 3⁄4-inch-thick disk and place on the prepared baking sheet.
Heat 1 tablespoon of olive oil and 1 tablespoon of butter in a large, nonstick skillet over medium heat; don’t let the butter smoke. In batches, cook the crab cakes for about 3 minutes on each side, turning once. Between batches, wipe the skillet with paper towels to remove burned crumbs and add fresh olive oil and butter.
Transfer the crab cakes to an unlined baking sheet and hold in the oven until all are cooked.
Put mayonnaise and sour cream into a bowl and whisk to combine. Add dill pickle relish, chili sauce, onion, parsley, seafood seasoning, mustard, and sugar. Stir to blend thoroughly. Cover and refrigerate until serving. Serve crab cakes with the sauce on the side.