Cook's Note: You can substitute queso fresco with any cheese you like, such as smooth goat cheese, feta, etc. You can stuff tamales with almost anything, pork, chicken, ground meat, etc.
For the stuffing: In a large skillet, saute the onions in the oil over medium-high heat until translucent, about 5 minutes. Add the mushrooms and garlic and continue sauteing until the moisture releases and completely evaporates, about 5 minutes. Season with salt and pepper. Remove from the heat. Add the cheese and herbs and set aside.
For the masa: Combine the masa harina with the stock and salt. Work in the lard until you get a spreadable consistency. If necessary, add a bit more stock.
To assemble the tamales: Drain and pat dry the corn husks. Spread the masa about 1/8-inch thick on each corn husk with your fingers, leaving about 1/2-inch border along the sides and a 2-inch border along the top and bottom of the husks. The key to good tamales is to spread the masa thinly. Then, use about 2 tablespoons/30 ml of the mushroom stuffing per tamale. Top with 2 to 3 poblano strips. Fold the sides until they just overlap, fold the narrow end under and place the tamales folded-side down in the steamer.
To cook, steam the tamales, covered, in a bamboo steamer over simmering water until the masa is no longer sticky, about 1 hour. (The tamales can be kept in the freezer for 3 months.)
Serve the tamales garnished with salsa, crumbled queso fresco and cilantro.