In a medium saucepan, heat 1-inch of water to a full boil. Add the frozen mixed vegetables, and return to a boil. Cook about 3 minutes, until crisp-tender (cooked completely, but retaining their green color and not mushy). While your vegetables are cooking, prepare your soy sauce gravy. In a small saucepan, mix 2 tablespoons cornstarch and 1 cup of water until smooth. Add 2 tablespoons butter and 2 tablespoons (minimum) soy sauce. You may adjust the amount of soy sauce to your taste. Place the soy sauce mixture over medium heat, and bring to a boil. Turn the heat to low, and cook the soy sauce gravy until it is thickened and rich-looking. By now, your vegetables should be done. Drain off the water and place the vegetables in a nice serving dish. You may serve this by pouring the soy sauce gravy over the top and mixing well, or by serving into individual bowls. In either case, you may optionally add a few cashews or chow mein noodle to the top for garnish