Gather and prepare ingredients for the filling
Peel and chop carrots, rinse under cold water, cover with cling wrap and microwave for 2 minutes, uncover, drain and set aside
Rinse red pearl onions and cover with cling wrap and microwave for 2 minutes, uncover, drain and set aside
Prepare mushrooms and pour 1 cup of frozen peas into a separate bowl and set aside.
Using the soup pot over medium high heat, melt 3 tablespoons of butter and add 3 tablespoons of flour and stir until the flour mixture turns a light brown.
Add warm chicken stock one ladleful at a time and stir with a wire whisk until 1-2 cups of the stock has been incorporated and you have a smooth sauce,
If the sauce seems a little thick, add more stock and continue to stir until it thickens again; you should have about 2 cups of sauce.
Now, add the reserved shredded chicken, carrots, mushrooms, onions and potatoes and bring all to a simmer.
Finally add the peas, check for seasoning and add salt and/or black pepper as needed.