Peel and dice <quantity>1</quantity> onion

Cut <quantity>2<unit>cups</unit></quantity> of portobello mushrooms into bite-sized pieces

Add vegetable oil to taste to a heated medium saucepan over medium heat. Add the mushroom and onion and sautée until tender and golden brown

Add <quantity>2</quantity> minced garlic cloves and stir

Add <quantity>½<unit>cup</unit></quantity> of white wine and stir

Season with salt and black pepper to taste

Add <quantity>1<unit>cup</unit></quantity> of heavy cream and <quantity>½<unit>cup</unit></quantity> of vegetable stock and stir

Dissolve <quantity>1<unit>tbsp</unit></quantity> of corn starch in <quantity>1<unit>tbsp</unit></quantity> of water, stirring until no lumps remain

Add the corn starch mixture to the sauce and stir until it thickens. The mushroom sauce is ready

Enjoy!