• Cut the roast beef into thin slices. An electric knife works very well for this job.
• Place the roast beef slices into roasting pot or dutch oven. Pour left-over roast au jus or prepared gravy mix over the beef. Warm in a 300 º F oven for 30 mins.
• NOTE: If the au jus is too thin, place it in a saucepan on the stovetop, bring to a boil whisk in about 1 tablespoon of gravy thickener or 2 teaspoons of cornstarch slurry. (cornstarch thinned with a bit of water). Cook until thickened.

Prepare the onion rings while the roast beef is warming.

• Heat the oil in a deep pot or use a deep fryer. (375º F)
• Thinly slice onion and separate into rings.
• In a medium bowl mix the flour, baking powder and salt.
• Dip the onion slices into the flour mixture to coat and set aside on baking tray.
• Make the batter: mix the egg and milk together, then add it to the remaining the flour mixture. Use a fork to whisk together.
• Dip the floured onions into the batter to coat, let excess drip off.
• Coat in panko bread crumbs after battering for extra crunch.
• Fry in batches until golden brown 2-3 minutes.
• Drain on wire rack or paper towel.
• Assemble by cutting thick slice of French bread, top with slices of roast beef, cover with gravy and top with onion rings.

Assemble roast beef sandwich

• Toast the bread slices, top with warm roast beef, gravy and crisp onion rings.