To cook the white rice, in a saucepan, add 1 cup of rice to 2 cups of cold water and bring to the boil. Reduce heat and simmer, covered for 25 minutes. Remove from heat and stand, covered for 5 minutes. If you would like to use a brown rice in this recipe, simply add an additional ½ a cup of water.
Meanwhile, heat half the oil in a large frying pan over a high heat. Cook meat in 2 batches, tossing quickly until browned. Remove from pan and set aside.
Reduce heat to medium-low and add remaining oil to pan. Cook onions for 5 minutes, stirring occasionally until soft. Add mushrooms and garlic. Cook, stirring occasionally for 5 minutes longer or until soft. Add paprika and stir for 1 minute.
Add stock, mustard, tomato paste, pepper and beef (with any juices). Simmer 3 minutes, stirring occasionally.
Place cornflour in a small bowl. Gradually stir in light thickened cream. Add to pan and stir just until thickened.
Serve stroganoff with rice, sprinkled with parsley and steamed green beans.