Heat a medium skillet over medium heat. Once hot, add olive oil. Add the onions and mushrooms to the hot oil. Sauté for 6-8 minutes, until the mushrooms release their juices and are tender.
Add the garlic and saute for another minute, until aromatic and browned.
Sprinkle in ¼ cup all-purpose flour. "Cook" until lightly browned, stirring with a whisk as needed. The oil, mushroom juices, and flour will combine into a paste.
Slowly pour in the vegetable broth while whisking consistently. Add the soy sauce, sage and freshly ground black pepper. Reduce heat to a simmer over medium-low. Continue to whisk the gravy occasionally to prevent a film from forming.
Simmer until the gravy coats the back of a metal spoon without falling off, or until desired thickness is reached. Taste for salt and enjoy!
Mushrooms: I prefer baby bella mushrooms for their flavor but white or cremini also work.Storage: Keep refrigerated for 3-4 days. You can freeze the gravy in a closed container for up to 3 months. Let thaw completely in the fridge before reheating on the stove or in the microwave.Gluten-free option: Make this recipe gluten-free by replacing soy sauce with tamari. Use a gluten-free all purpose flour mix, such as Bob’s Red Mill, in place of standard all-purpose flour.