Position a rack in the center of the oven; preheat to 400 degrees .
Drizzle the garlic with EVOO; season with salt and pepper. Wrap in foil; roast until tender and caramel in color, about 40 minutes. When the garlic is done, reduce the oven temperature to 325 degrees .
When cool enough to handle, squeeze the roasted garlic into a bowl; mash to a paste. Add the butter, rosemary, marjoram and thyme; season. Coat the roast with the herb butter; stand it up in a roasting pan.
Cook the roast until it registers 125 degrees to 130 degrees on an instant-read thermometer (for medium-rare), about 2 3/4 hours. Let the roast rest, covered with foil and a kitchen towel, for 1 hour. Carve and serve with Mom's Horseradish Sauce.