There's so much more to venison than tenderloins or burger. Many people don't realize that venison can be roasted successfully without making it tough or leathery; the key is to provide some of the fat that this extra-lean meat doesn't usually contain, and to sear the meat first before following it up with a slow roast at lower heat. I hope you enjoy it.
Preheat the oven to 450 degrees F (230 degrees C). Spread garlic all over venison roast, season with salt and pepper, and place in a roasting pan.
Heat butter in a skillet over medium-low heat and cook and stir 1/2 cup onion, cilantro, sage, and basil until onion has softened and turned translucent, about 5 minutes. Spread the butter mixture evenly over the roast.
Roast in the preheated oven for 20 minutes. Add remaining 2 cups onion, orange juice, and cranberries to the roasting pan; reduce oven temperature to 325 degrees F (165 degrees C). Continue to roast, basting frequently, until a meat thermometer inserted into the thickest part reads 140 degrees F for medium rare, about 1 hour. Remove the roast from the pan; cover to keep warm while you prepare the sauce.
Pour beef stock into the roasting pan, and bring to a boil while scraping the browned bits of food off the bottom of the pan with a wooden spoon. Continue boiling until the liquid is reduced by half, about 10 minutes. Skim off any fat; stir in the jelly and sherry. Continue to boil until the sauce is slightly thickened and evenly coats the back of a spoon, about 3 minutes. Season with salt and pepper.
Trying this in a slow cooker will make the meat stringy and tough, so in short, don't do it. This should end up just as tender and sweet as tenderloin.
I cook my roasts to medium-rare. I don't care for them done any more than that, so if you like yours medium well or more, just be careful not to overdo it.
Fresh sage and basil can be substituted for the dried herbs. Just use twice the amount of each.