Preheat oven to 250 degrees. Line a large baking pan or Dutch oven with aluminum foil.
Place corned beef on foil (set aside the little seasoning packet**), fat side up and place onion slices over the top. In a small bowl, mix together cola, juice, Worcestershire Sauce and cinnamon. Pour around corned beef. Completely seal foil around pan. Bake for 6 – 7 hours or until fork tender.
Near end of baking time, in a small sauce pan, mix together brown sugar, honey, mustard, chili powder and garlic. Heat over low heat until sugar is melted.
Remove brisket, raise oven temperature to 400 degrees, open foil and baste brisket with sugar/honey mixture, do not recover.
Return to oven and bake for another half hour, basting once during that time.
Remove to platter, cover with foil and let rest for 15 to 20 minutes before slicing. Cut the corned beef against the grain into ½ inch slices.
*I choose the flat cut over the point cut, because I find it less fatty. I think it is a better cut for corned beef. I use the point for braised brisket because it shreds more easily.
**Now, what to do with that seasoning packet….if you are boiling cabbage, carrots and potatoes, place the seasoning packet in the liquid you use for preparing the vegetables.