To make the marinade, add soy sauce and vinegar to blender, replace lid and turn on blender. Through the feed opening add, 1 at a time, the garlic, ground cloves, thyme, black pepper, mustard and molasses. Place flank steak in a nonreactive container, add marinade and coat steak. Cover and refrigerate for at least 2 hours.
While the steak is marinating, roast the garlic for the demi-glace. Pre-heat oven to 350 degrees F. Cut root end from end of head of garlic and use a piece of heavy duty aluminum foil to mold an enclosure around the garlic to include a base to keep it from tipping over. Pour 1 tablespoon of the grapeseed oil over the garlic from the root end so the oil flows between the papery skins and the cloves, reserving the rest of the oil for sauteing the shallots. Roast for 40 minutes to 1 hour, being sure to monitor so the garlic doesn't burn. Remove from oven and let cool to room temperature.
To make yuca, boil until tender in enough water to cover. Drain well, rinse and set aside briefly. Make a dressing by adding vinegar, salt and thyme to a blender and adding the olive oil in a slow thin stream through the feed opening with the blender running. Mix yuca with enough dressing to coat and refrigerate.
Heat grill (or use grill pan). Remove steak from marinade, discard marinade, and sear each side of steak. Cook to your desired level of doneness and transfer to a cutting board to let rest for 5 minutes.
To complete the demi-glace, heat the remaining tablespoon of grapeseed oil in a skillet over medium-high heat. Add shallots and saute until translucent. Deglaze pan with wine and allow most of it to evaporate. In a small bowl, whisk together water and beef base and add to pan. Squeeze the roasted garlic cloves directly from their skins into a small bowl and mash them. Add the roasted garlic to the pan and stir until it is integrated with the rest of the contents of the pan. Allow to reduce by half. Season with salt and pepper, to taste, remove from heat and keep warm.
Slice steak on the bias into 1/4-inch thick strips and arrange on plate alongside yuca. Spoon sauce over steak. Garnish with minced parsley.