03When pork is browned, transfer it to a plate and discard fat that's in casserole. Reduce heat to medium, and add butter to pan. When it is foamy, add garlic cloves. Stir until lightly browned on edges. Add sage leaves, and stir to coat. Put pork back in casserole, and pour in enough of the warm milk mixture to come 1/2 to 2/3 up the sides of pork. Bring to a simmer, add lemon zest and season to taste with salt.04Partly cover, and simmer until an instant-read thermometer registers 140 degrees (about 15 to 30 minutes; cooking time will vary according to shape of roast and degree of browning). Liquid will form a skin and custard around pork. Shut off heat, and allow to cool. Cover, and refrigerate until shortly before serving.05To serve, remove pork from milk mixture and carve into 1/8-inch slices. Meanwhile, place casserole over medium heat and reduce liquid to a soupy custard. While the liquid is still a little loose, return sliced pork to casserole and spoon sauce on top. Allow pork to heat through. Serve, spooning some custard, lemon zest and sage on top and sprinkling with coarse salt.