For Arby's Cheese Sauce:
In a small saucepan, heat medium-low heat. Combine the cheddar cheese (4 oz), American Cheese (4 oz cut into cubes), 1/3 tsp of paprika and half and half (1/4 cup).
Cover the lid, and stir every 5-6 minutes to combine the ingredients nicely. Set at the lowest temperature while you prepare the rest of your ingredients.
Place buns on a baking tray.
Spread beaten egg white on top of the buns using a brush. Sprinkle with poppy seeds and chopped onion, and bake for about 5 minutes.
For the Arby's Red Ranch Sauce
Heat up the 1 Cup of ketchup, 2 TBSP of apple cider vinegar, 2 tsp of sugar, 2 tsp of paprika, 1 tsp of garlic powders, 2 tsp of salt and 4 TBSP of water
Allow the saucepan to simmer on medium heat for approximately 5 minutes.
Turn the heat off, and add in the 2 tsp of mayonnaise and stir until well combined.
Assembling Arby's Beef and Cheddar Sandwich:
Start by topping the bottom bun with Arby’s sauce. Next, add roast beef to the pile. Finally, spoon on cheddar cheese sauce and then more Arby’s sauce.