Line a baking sheet with aluminum foil and set aside.
In a medium bowl, whisk together egg, mayonnaise, Harissa, and scallions.
Squeeze out all water from the crab meat (important!)
Gently stir the crabmeat into the mayo/harissa mixture.
Form crab mixture into 4 patties, about ½ cup each and place on prepared baking sheet. Cover and refrigerate for at least 1 hour (refrigerating them is optional, but it does help the patties hold together).
Heat butter in a non-stick skillet over medium heat.
Place patties in skillet, and cook until golden brown, about 5 to 6 minutes on each side.
Resist the urge to move or mess with the cakes while they are cooking or they will break into a hash-brown-like mess. If this happens, well the crab hash is still tasty!
Serve immediately, with lime wedges for a little garnish and hit of citrus.