Prepare it in two large stockpots or Dutch ovens rather than one.
Brown the mushrooms in batches so they caramelize instead of steaming.
Cook the noodles directly in the broth as directed, but stir frequently to prevent sticking.
Stir in the sour cream only after removing the pots from the heat to prevent curdling.
If holding for a buffet, keep warm over low heat and stir occasionally. You may need to add a little extra warm chicken broth if it thickens too much.
