Preheat the oven to 325°F. Using a sharp knife, slice off about a quarter-inch off the top of the head of garlic. Don't be too concerned if the smaller cloves are still completely intact. Place in a ramekin, drizzle the top with a little olive oil, cover the ramekin with foil, and roast in the oven for 1 hour. (You might want to roast some more garlic together with this one for other purposes; just use a bigger roasting pan.) Let the garlic cool and set aside.
In a heavy-bottomed medium saucepan, combine all of the remaining ingredients (water to cayenne pepper). Squeeze out all the soft fleshy roasted garlic insides into a small container (just to make sure none of the garlic skins go into the sauce) and add it all to the saucepan. Give the sauce a stir and set it over medium-high heat, stirring occasionally until it comes to a boil. Reduce the heat to a simmer (very low heat) and keep simmering, stirring occasionally, for about 45 minutes, or until the sauce is reduced to a third and is thick and syrupy.
This glaze doesn't need to be brushed over the meat before going on the grill (the high sugar content will cause it to char). Just brush it on the meat after it's off the heat. Serve on the side as well.