Grilled Fillet Mignon with Creamy Mushroom Sauce

This is the best mushroom sauce that I ever tried. My friend Marina shared this recipe with me and I want to share it with you.It goes great with Filet Mignon but you can have it with any other type of steak or even chicken.
Ingredients:

Serves 6-8 people
6-8 Filets
10-12 ozs button mushrooms sliced
1 onion chopped
1/3 cup white wine
1 pint heavy whipping cream
1 tablespoon demi glace *
salt and fresh crushed pepper
3 tablespoons olive oil

* You can make it yourself (which takes like over 20 hours to cook) or you can buy it online or in the store. I bought mine at William & Sonoma for $29.99, It's pricy but really worth it.

Directions:
Heat a saute pan med-high heat and add olive oil.
Add mushrooms and onions, and saute until onions are soft and liquid is gone.
Remove about 4 tablespoons of mushroom and onion and reserve it for later. 
Add white wine and let it evaporate. 2-3 minutes.
Add cream and simmer for about 5-7 minutes.
Stir in demi glace.
Add salt and pepper to taste.
Using a hand or mini blender, pulse the sauce.
Add the reserved cooked mushrooms, mix and serve over grilled filets.

If the sauce is to thick, add more cream and reheat it.