Wash and cut your carrots, celery, onion, potatoes and parsley. Cut the carrots into half circles, celery and onion into a small dice, and the potatoes into a medium to large dice. Roughly chop the parsley leaves into small pieces.
In a large pot, add some oil over medium high heat. Add in the onion, celery, and carrots and cook to develop some color, around 5-8 minutes.
Once the vegetables have developed some color, make some room in the middle of the pot and add the beef. Brown the meat as best as you can.
Once the beef has cooked, add in the potatoes, broth, and enough water to just cover the contents of the pot. I used 2 cups, you may need more or less. Reduce the heat to medium, cover the pot and allow it to boil until the potatoes have softened, around 10 minutes.
When the potatoes have about 5 minutes left, start making your bechamel sauce. If you have never done this before, I recommend watching a quick tutorial on how to do it. Here is Papa Gordon making one, https://www.youtube.com/watch?v=9aeCJGmEXqE
In a skillet over medium heat, make a roux by melting the butter and stirring in the flour. Add in the milk in batches, stirring constantly until a smooth sauce forms and it begins to thicken. Once smooth, add in the cheese and melt.
Pour in the cheese sauce to the pot with the soup and mix.
To thicken the soup you will want to add a cornstarch slurry, mix 1 tbsp of cornstarch with 1 tbsp of cold water together at a and stir it into the mixture until you have achieved your desired thickness. I used 2 tbsp when I made it but depending on how much liquid you have, you may need more or less.
Stir in 1 tbsp of granulated chicken bouillon and salt and pepper to taste. Add in ¼ cup of chopped fresh parsley if you wish.