Hot Roast Beef Sandwich

Ingredients

• onion rings
• 1 onion large, cut into thin slices
• 1 1/4 cups flour all-purpose
• 1 teaspoon baking powder
• 1 teaspoon salt
• 1 egg
• 1 cup milk or as needed
• 3/4 cup panko bread crumbs
• 2 cups canola oil for frying, or as needed
• sandwiches
• roast beef Leftover, from my Slow Cooker Roast Beef recipe
• au jus
• roast
• french bread cut into ¾ inch slices
• thickener *gravy, if needed