Thai Sausage Soup

I don't know how authentic this is, but it tastes really good and it's very easy to make. 

1 Lb
Italian sausage, removed from casings
onion, chopped
celery, very thinly sliced
8 cups
chicken stock
1 Tbl
hot & sour paste (Tom Yum paste)
 1 Lb
fresh mushrooms, sliced
15 oz can
coconut milk
1 tsp salt

lime, juice only
12 oz
rice stick noodles

black pepper

green onions, chopped (green & white parts)

a large pot over medium heat.  Add the sausage and cook until browned, breaking it up as you cook it.   Add the onion and celery and cook for 5 minutes.  Add the chicken stock and bring to a boil.  Decrease the heat and simmer for 10 minutes.   Add the sugar, hot & sour paste, mushrooms, coconut milk, and salt.  Bring the soup back to a simmer and cook for 2 more minutes.  Add the lime juice and season to taste with salt & pepper.  Turn the soup off, add the rice noodles, wait 7 to 8 minutes,  Stir to mix the noodles in and serve garnished with green onions.