For the sandwich, you will need one, to two slices per serving of bread. The larger the slices of bread you are able to purchase the better your meal will be.
Once your beef is cooked, remove it from the oven and allow it to cool. Drain the juice from the roast into a saucepan.
In a cup, add flour or corn starch to the bottom, then take a scoop of your beef broth, and mix them together. You will get a really thick mixture. Add more juice to the cup until it becomes like thick gravy. Pour this cup full into your saucepan and whisk until there are no more lumps. If you have lumps that just won’t go away, you can pour your gravy into your blender and mix for a few minutes. If there ended up being too much flour and your gravy is too thick, you can add water and a cube of beef bouillon to help thin out the gravy but still keep the taste.
Now that all of your components are made, it is time to assemble your Beef Manhattan! Start by putting a slice of bread on your plate. Next, add ½ to ¾ cup of your cooked roast on top of the bread. Top with a scoop of mashed potatoes and drizzle gravy over the entire dish. Serve while hot and enjoy!