Chop the lemongrass into 2 inch pieces and then slice down the center, add to the soup pot along with the broth and coconut milk, garlic and ginger. Bring to a boil and them simmer on low for 30 minutes. Once the broth is done simmering you will want to strain it through some cheese cloth. The lemongrass stalks are not edible, I found that out the hard way.
Bring the broth back to a simmer and add the tofu, mushrooms, snow peas and the rice noodles.
You can add the lime juice at any time.
I added some lime juice at the beginning and then some at the end before serving.
Simmer until the noodles are soft.
Garnish with grated ginger or scallions.