Bring a large pot of water to a boil for the pasta. Once boiling, add the bowtie pasta and continue to boil until tender (about 7 minutes). Reserve 1/2 cup of the starchy pasta water before draining in a colander.
While the pasta is cooking, prepare the rest of the dish. Wash and slice the mushrooms, then add them to a large skillet along with the olive oil. Sauté over medium heat until the mushrooms have released all their water, the water has evaporated, and the mushrooms begin to brown (about 7 minutes).
While the mushrooms are cooking, mince the garlic. Add the garlic and butter to the browned mushrooms and continue to cook over medium for 1-2 minutes more, or just until the garlic softens a bit.
By this time the pasta should be finished cooking. Add about 1/4 cup of the reserved pasta water to the skillet and stir to dissolve any browned bits off the bottom of the skillet. The starchy pasta water and butter will make a slurry that will act as a light "sauce" that helps the salt and pepper adhere to the surface of the pasta.
Add the fresh spinach to the skillet and stir just until wilted (1 minute). Add the drained pasta to the skillet and stir until everything is evenly combined. Turn the heat off and season liberally with salt and pepper. If the pasta is dry, you can add an additional splash of the reserved pasta water.
Finally, spoon the ricotta on top of the pasta in one-tablespoon dollops. Add a pinch of red pepper on top, if desired, and serve warm.