Thoroughly wash mushrooms under cold water, pat them dry, and cut the same as the onion. Into the smallest pieces, you can. Add to the skillet and cook for 5 minutes.
Take the separate skillet and make the sauce. First, add flour and fry it until the color becomes creamy.
Add butter to the skillet, and stir constantly until the mixture becomes like in the picture I have.
Add cream; keep stirring the mixture until it becomes smooth, and try getting rid of all the lumps. Cream is a great way to soften the taste of mushrooms.
Stir the mixture and cook it for at least 5 minutes at low heat in a skillet covered with a lead. Season sauce to your taste with salt and pepper. If you like some special type of herbs, add them to the sauce. I tend to use dry basil, thyme, or rosemary.
After seasoning take the skillet off the heat and let it sit for 10 minutes to incorporate all the flavors and then serve. Enjoy!