I used a combination of Shiitake mushrooms, Maitake mushrooms (a.k.a. Hen of the Woods), and Eryngi mushrooms (a.k.a. King Trumpet) in equal parts. Both the Shiitakes and Maitakes taste meaty, and when they're caramelized, they come together to create a rich, savory flavor that tastes like a good piece of roasted meat. Eryngi mushrooms, on the other hand, don't have much of a flavor at all, but the large stems have a fibrous texture that mimics the muscle fibers in meat.  As flavorful as this mixture is, I still wasn't happy with the level of umami in the finished vegetarian Mapo Tofu. To amp this up, I started adding dried shiitake mushrooms to the mix. Dried Shiitakes contain fifteen times the concentration of glutamates of fresh shiitakes, and it works out well because we need a broth to replace the chicken stock anyway. When you rehydrate the mushrooms, they infuse the soaking liquid with their flavor, which makes for a fantastic broth.