Preheat the oven to 425°F or 220°C.
Prepare the shredded beef according to my Slow Cooker French Dip Sandwiches recipe, in advance. Reserve 2 to 3 cups of the cooked meat for the fries.
Cut the russet potatoes into thick, evenly sized steak fries. Don't cut too thinly here as they might soften too much in the oven. For crispier fries, place the potatoes in a bowl of ice water with the white vinegar. Soak for 30 minutes to one hour, then drain and dry the potatoes completely on a clean kitchen towel.
Place the potatoes on a large sheet pan. Add the cooking fat and salt, then toss until the fries are evenly coated. Arrange them in a single layer. Bake for 25 minutes on an upper-middle rack.
Thinly slice the onion and peppers into half rounds. For extra flavor, cook these on a skillet with a drizzle of olive oil and a pinch of salt until lightly browned and softened.
Remove the pan from the oven and flip the fries. Scatter the sliced bell peppers and onion around the potatoes. If the vegetables haven't been cooked beforehand, toss them in some of the remaining oil on the pan to coat them. This will help them cook and brown more evenly in the oven.
Return the pan to the oven and bake for another 25 minutes, or until the fries are golden and the vegetables are tender.
Remove the pan from the oven, scatter the shredded French dip beef evenly over the potatoes and vegetables. Tear the provolone slices into smaller pieces and arrange them across the entire sheet pan.
Bake for another 10 minutes, until the meat is hot and the cheese has melted.
Turn on the broiler and broil for 2 to 3 minutes, watching closely, until the cheese is bubbly and the edges of the meat are lightly crisp.
Serve immediately with warm au jus for dipping or drizzling, if desired.