1/2 cup soy sauce
1/5 cup red wine vinegar
1 tablespoon vegetable oil
1/2 cup brown sugar
1/2 cup distilled white vinegar
In a small bowl, mix soy sauce, vinegar, oil and brown sugar. Stir until soy sauce is completely dissolved. Cover and refrigerate for at least one hour. The steaks will require an occasional stirring to keep them from browning.
Pour soy sauce mixture over the steaks and pour marinade over all. Place steaks in a shallow dish or bowl, and sprinkle with the sugar. Shake to coat. Cover and refrigerate for several hours or overnight.
The steaks will continue to brown well. Shine the marinade over all steaks during cooking. Cover and refrigerate steaks or marinate for 24 hours in the refrigerator.
When the steaks are cool, the marinade should be well absorbed but do not soak in. Using a dry brush, dust the steaks with powdered sugar and stick the golden edges with toothpicks. Form steaks into patties using tongs and remove from marinade. Cover with plastic wrap and refrigerate overnight.
Heat a medium skillet over medium heat. Fry patties on both sides until mustard is emulsified and slightly browned. Flatten on both sides and serve hot.