Preheat your Yoder Smokers YS640s Pellet Grill to 450ºF, with the diffuser door removed for direct grilling.
Preheat a large Lodge Enameled Cast Iron Dutch Oven over the direct flame for 5 minutes.
Combine all ingredients for the beef stock in a Finex Cast Iron Dutch Oven. Cover with a lid and transfer to the grill. Slide the larger empty dutch oven to the indirect side of the grill and place the beef stock over the direct heat.
Place the butter and beef tallow in the empty dutch oven. When melted, add the thin sliced onions. Season with R Butts R Smokin’ R Beef Rub and toss to coat. Cook, stirring occasionally, until the onions are completely softened and caramelized (browning). This may take a couple of hours.
*When the beef stock is simmering, you can rotate the two dutch ovens to allow the onions to brown quicker, but be careful not to scorch the onions.
*The beef stock will naturally reduce while simmering, even with the lid on. When the short rib in the stock is fully tender and the meat is falling off the bone, strain the stock. Keep and shred the meat from the short rib, but discard the rest of the solids. You’ll need two quarts of beef stock for the French Onion Soup. If the stock has reduced to produce less that two quarts, top off the stock with water.
When the onions are fully caramelized, add the garlic and cook for a minute. Add the dry sherry and allow the liquid to reduce until almost entirely gone.
Add the flour and cook for a couple of minutes, stirring frequently.
Add the Worcestershire sauce and two quarts of beef stock. Add the shredded beef short rib. Bring to a simmer and let cook to slightly thicken, about 10-15 minutes. Taste and adjust seasoning as needed.
Place baguette slices in a mixing bowl and drizzle with Saica Sicilian Extra Virgin Olive Oil. Toss to coat. Arrange on a sheet pan in a single layer. Transfer to the indirect side of the grill (on the right), and cook until lightly toasted, about 15 minutes.
Ladle one cup of the French Onion Soup into a soup crock. Top with two slices of toasted baguette and one and a half ounces of grated Gruyere. Place under a broiler to melt the cheese and toast the top, or do the same with a propane torch.