Servings: Serves 8
To make tartar sauce: Whisk all the ingredients in a medium bowl to blend. Season with salt and pepper. Cover and refrigerate at least 1 hour and up to 2 days.
To make the sandwiches: Line a baking sheet with waxed paper. Whisk the first 8 ingredients in a large bowl. Mix in the crabmeat and 1 cup of panko, breaking up the crabmeat slightly. Let stand 15 minutes. Place the remaining panko on a small rimmed baking sheet. Form the crab mixture into 8 3-inch-diameter patties. Press both sides of the patties into the panko. Transfer the patties to the waxed-paper-lined baking sheet. Cover and refrigerate at least 1 hour and up to 1 day.
Melt 1 tablespoon of butter with 1 tablespoon of oil in each of 2 heavy large skillets over medium-high heat. Add the crab cakes to the skillets and cook until golden on both sides, adding more butter and oil as needed, about 5 minutes total.
Meanwhile, melt 2 tablespoons of butter on a flat griddle pan over medium heat. Set the buns on the griddle, cut side down, and cook until heated through and toasted on the bottom.
Set the crab cakes on the bottoms of the toasted buns. Top with the tartar sauce, then mixed greens and the bun tops.