Remove stem of mushrooms and clean them with a damp paper towel. (Washing them under water can make them turn slimy.)
Heat 2 tbs oil in a skillet or frying pan on a medium/low flame.
Add the sliced garlic and mushrooms and and cook for about 2-3 minutes a side (for bite size mushrooms - more for larger ones) until they are still a little crunchy but not raw. Taste one to check if they are to your liking.
Add 4 tbsp Balsamic vinegar, mix well and cook for 3-4 minutes to reduce the liquid to half the volume. The idea here is to cook off the tanginess of the vinegar until it is sweet and slightly syrupy.
Turn fire off and finish by quickly blending in a tablespoon of cold butter.
Add salt and ground black pepper to taste, plate the dish, garnish with parsley and serve.