Dice onions, slice mushrooms, peel the garlic, and set it all aside. Measure the rest of ingredients and set it aside as well.
Preheat a large, preferably bottom heavy cooking pan, over medium heat and add butter.
Once butter is melted, add onions and saute until it starts to brown.
Press in garlic and saute for just a few seconds, until garlic is fragrant.
Add mushrooms and saute for a few minutes, stirring once in a while.
Sprinkle flour all over the mushrooms and stir well to coat it all in flour evenly.
Slowly pour in beef stock while gently stirring. Keep stirring slowly as the flour mixes in smoothly into the stock and thickens.
Add seasoning and let the mixture gently simmer while it thickens. Once thickened, take the pan off heat and it's ready to serve.
Notes
*Gluten Free Notes: use gluten free all purpose flour of needed. Try to get 1:1 gluten free all purpose flour, NOT almond or coconut.
Make Ahead: You can prepare it a day before and store it in the refrigerator, in a food storage container with an air-tight lid.
To reheat gravy: it's best to do it on the stove in a bottom-heavy sauce pot. Set heat to medium to medium-low heat and reheat just until heated through. Remember to stir a few times to ensure even heating.