I modified a recipe from Heidi Swanson's Super Natural Everyday, and I think I might have come close to Khao Soi! The Khao Soi connoisseur is at summer camp--I will await her blessing before crying victory. You can find most of these ingredients at a good grocery store or an Asian grocery. The red curry paste is one of the hotter curries so be careful.
I used full-fat coconut milk, but you could use light--it won't be a thick and creamy. I like the Chakoh brand the best but Polar was available at my grocery store.
I got a bag of shallots at Tim's Oriental Market--much cheaper than buying at the grocery store, and look like a slightly different variety. If you live in the San Antonio area Tim's is worth a trip.
It is also worth the effort to find and use Thai basil. Sweet basil will substitute, but Thai basil has a distinct flavor that really completes this soup. I bought a plant at the farmer's market. You can also buy seeds on-line if you want to grow your own. Probably won't help you if you want to make this recipe tonight, but truly worth it if you want authentic Thai flavor.
These are the same noodles used in Pad Thai. Again, easy to find in any Asian market or well-stocked grocery store. I bring a pot of water to boil, turn off heat and add noodles. Soak for 5-10 minutes, drain and rinse with cool water. I don't recommend adding them to the soup because they will get too mushy. I just put them in a bowl and then ladle soup on top. If you have leftovers keep the noodles separate.
1 lb sirloin steak, cut into 1" cubes
2 TBS red curry
3 large shallots, chopped
3 medium zucchini or other summer squash, cut into chunks
4 cloves garlic, chopped
1 can coconut milk
1 can beef broth
1 bunch Thai basil
Season the meat with salt and brown in coconut oil. Remove and set aside. Add a little more coconut oil to skilled and cook curry paste over medium heat until fragrant. Stir in shallots and cook til tender. Stir in squash and garlic. Saute briefly, until coated with curry mixture, then add coconut milk and broth. Bring to a boil, then lower heat to simmer--add meat. Cook til slightly thickened. Check seasoning and add salt/curry paste if needed. Just before serving, add 1/2 cup whole basil leaves. Serve over noodles. Even better the next day.