Slice large mushrooms in half, leave the rest whole.

Saute mushrooms in a pan on low-medium heat with 1-2 tbsp butter.

Once mushrooms have nearly finished sauteing, give a light sprinkle of thyme, sprinkle some garlic powder, and salt & pepper to taste. Stir spices in.

Pour in beef stock and white wine vinegar (could also use red wine vinegar, or wine if it's handy!).

Add some Worcestershire sauce (about 4-5 drops, more if you like).

Cook mushrooms until stock has reduced and thickened.

Now for the sandwich!

Butter all sides of your bread.

Place layer of grated Swiss cheese on bread.

Top with mushrooms.

Add another layer of Swiss Cheese and top with bread.

In a pan on medium heat (lower heat if your bread is browning, but cheese isn't melting enough), cook grilled cheese until golden brown and cheese is melted.

Dig in!