In a small mixer bowl at low speed, beat pork, 1/4 cup flour, egg, minced onion, salt, coriander, sage, thyme, and 1/8 teaspoon pepper just until blended. Slowly add 1/2 cup water and beat until mixture is smooth and light.
In a large skillet over medium-low heat, heat 2 tablespoons of the margarine until foam subsides. Drop about 1/4 cup of the pork mixture at a time into skillet and shape into patties about 1/2 -inch thick. Sauté 7 minutes or until a rich medium-brown crust forms. Turn patties and cook 7 minutes longer or until no longer pink in the center. Drain on paper towels and keep warm.
In a medium saucepan over medium heat, sauté chopped onion in 1 tablespoon of the margarine 3 minutes. Add mushrooms and sauté 2 minutes longer. Remove to a small bowl; set aside.
In the same saucepan over medium heat, melt remaining 2 tablespoons margarine. Add 2 tablespoons flour. Cook and stir 1 minute or until lightly browned. Stir in 1 1/2 cups water, bouillon granules, and 1/8 teaspoon pepper. Stirring, bring to a boil and boil 3 minutes or until thickened. Remove from heat. Return onion and mushrooms. Stir in sour cream until blended. Cook over low heat just until heated through (do not boil).