Put the milk into a small heavy saucepan. Add the roux cubes and heat, stirring regularly, until it starts to boil and the sauce thickens. Removed from heat. Stir in the mustard, and the prepared cubed cheese until moderately smooth.
Pour about a quarter of the sauce into the bottom of a 1 quart baking dish. Carefully spread the rice into the sauce so that it covers the bottom of the pan. Layer the ham, and then the kale over the rice, distributing each evenly.
Carefully pour the rest of the sauce over the casserole.