Mix mashed potatoes, milk powder, mushrooms and thyme in a small zip-lock freezer bag.
Pack remaining ingredients separately.
Pour dry soup mixture into the pot; add 1 cup water and stir well.
Let stand 5 minutes.
Place pot over medium heat and bring to a boil.
Season to taste with salt and pepper.
Put in bay leaf and simmer, stirring, for 5 minutes.
Remove from heat and discard bay leaf.
Serve with croutons.
