Balsamic Steak Gravy with Portobello Mushrooms

Prepare balsamic mixture first. Pour vinegar, olive oil, Dijon Mustard, lemon juice, salt, and sugar into a salad oil shaker and shake vigorously until well mixed. Set aside. On medium high heat, melt butter in a large non-stick frying pan. When the butter is melted, add the mushrooms and garlic. Place the cover on the pan and saute for two minutes, stirring occasionally. Add the balsamic mixture, fresh basil and oregano to the pan. Stir, cover, and let it simmer for about a minute. Mix the water with the cornstarch in a small cup or bowl and stir until dissolved. Add it to the pan, stir it into the mixture and turn heat down to low. Stir until the sauce thickens. Cover and continue to simmer on low heart for another 2 minutes or until the mushrooms are cooked to your liking. Add freshly ground pepper to taste.