In cooker, heat 2 tablespoons of butter over medium heat. Saute onion for 4-5 minutes until soft. Stir frequently so onion does not brown. Add rice, and saute until light brown. Add peas and chicken stock, stir well. Close lid and bring to pressure. Lower heat and cook for suggested time. See times below. Release pressure and open the lid. Stir in additional one tablespoon of butter, Parmesan cheese and pepper. Let sit until butter and cheese melts. Stir thoroughly and serve.