Put the corned beef in a large pot with the onions, carrots, and thyme.
Cover with water, bring to a boil, and simmer for 2 hours 30 minutes.

Glaze:
Put the orange marmalade and whiskey in a saucepan. Bring to a boil and reduce until the liquid has completely evaporated (about 7 minutes).
Remove from heat and add the nutmeg and Dijon mustard.

Preheat the oven to 425 F (205 C).
Place the corned beef and carrots in a greased oven-safe dish.
Brush the meat and vegetables with the glaze and bake for 35 minutes.
Serve the corned beef, sliced against the grain, with the carrots and Dijon mustard.