Here is a simple recipe for mushroom sauce:

1. Roast mushrooms and garlic in oil until they are cooked.
2. Add salt and black pepper powder.
3. Let the mushrooms cool down and grind them with water to make the mushroom sauce.

Here is another recipe that you might find useful:

1. Melt butter in a large pan over medium heat, then add garlic and onions and fry until soft.
2. Add mushrooms and continue to fry for another 2 minutes, or until they begin to soften.
3. Sprinkle flour over the mushrooms and stir well. Some of the flour may stick to the base of the pan - that's okay.
4. Gradually pour in milk while stirring constantly until the sauce thickens.
5. Add salt and black pepper powder to taste.