Peel and trim the carrots. Slice on the bias into 1/4-inch thick coins and place them in a large skillet.
Sprinkle with the salt and add water until barely covered. Bring the mixture to a boil, then reduce the heat to medium.
Cover and cook until the carrots are tender but still hold their shape, 8 to 12 minutes (do not overcook). Drain well and set aside.
Add the butter and marmalade to the pan and cook over medium heat until liquified.
Stir in the mustard and add the carrots back to the pan. Continue cooking, gently turning the carrots with a spatula, until they are well coated with the glaze.
Transfer to a covered casserole and keep warm until ready to serve.
Notes
Make-Ahead Instructions
This recipe may be made ahead and reheated. Remove the casserole from the refrigerator 30 minutes in advance, then heat, covered in a 325°F oven for 25 to 30 minutes.