In a saucepan over medium heat, heat the oil. Add the onions, mushrooms, garlic, bay leaves, and oregano. Saute onions for about 2 to 3 minutes or until they become translucent and tender. Remove the bay leaves.
Add the flour and mix to form a thick paste. Allow to cook, stirring, 1-2 minutes until golden.
Add the vegetable broth, stir, and bring to a simmer over medium heat. Season ground pepper.
Use a whisk to gently mix the gravy until it thickens to your desired consistency, about 20 minutes. If you prefer a thinner gravy, mix in 1 to 2 tablespoons of water.
If you’re using cornstarch: While you can add it the same way as you would the flour (sprinkled into the pan). We like to create a cornstarch slurry by combining the powder with a few spoonsful of water and whisking well until it’s lump-free. Then add that to the gravy mixture. Stirring constantly, cook until the mushroom gravy has thickened, and then serve! This should only take minutes.
To caramelize the mushrooms: For more depth of mushroom flavor, first pan-fry the mushrooms with no oil to allow them to release their excess liquid and start to brown. Don’t stir them too much during this time (this can take 10-15 minutes). Then continue with step 2 above.
Adjust the texture: We love this chunky mushroom onion gravy as is. However, if you prefer smooth gravy, you could use a blender/immersion blender to blend it until it’s smooth (or your texture of choice). Add a little extra stock then, if preferred.