1 pound fresh lump crab meat
1 Tablespoon Dijon mustard -- optional
2 Tablespoons flour -- more for dredging
2 tablespoons extra virgin olive oil
4 tablespoons butter
Salt and freshly ground black pepper
Gently combine crab, egg, mustard, salt, pepper and 2 Tablespoons flour. Cover; and put in freezer for 5 minutes. Shape mixture into 4 hamburger-shaped patties. Line plate with plastic wrap, and put crab cakes on it. Cover with more plastic wrap, and refrigerate for about 30 minutes (or as long as 1 day), or freeze for 15 minutes.
Put flour for dredging in a bowl. Combine oil and butter in 12-inch skillet, and turn heat to medium. When butter melts and its foam subsides, gently dredge a crab cake in flour. Gently tap off excess flour; and add crab cake to pan; repeat with remaining crab cakes, and then turn heat to medium-high.
Cook, rotating cakes in pan as necessary to brown first side, 5 to 8 minutes. Turn and brown other side (it will take slightly less time). Serve hot, with lemon wedges.