1. Preheat oven to 350°F. Cut 2 (25x12-inch) pieces of foil. Slightly crush each sheet to make a 3 1/2-inch ball; flatten balls slightly. Place on ungreased cookie sheet. Press or roll each biscuit to 6-inch round. Place 1 biscuit round over each foil ball, shaping biscuit gently to fit. Bake 8 to 12 minutes or until golden brown. Cool 5 minutes. Remove biscuit cups from foil balls.
2. Meanwhile, in 2-quart saucepan, melt butter over medium-high heat. Add onion and mushrooms. Cook and stir 5 to 7 minutes or until vegetables are tender. Stir in soup. Reduce heat to medium; cook about 4 minutes, stirring occasionally, until hot.
3. In small bowl, stir water, cornstarch and pepper until smooth. Increase heat to medium-high; stir cornstarch mixture into soup mixture in pan, cooking and stirring until mixture boils. Cook, stirring constantly, about 1 minute or until mixture is slightly thickened.
4. Place biscuit bowls in individual shallow soup bowls; spoon half of the beef stew into each. (Some soup may flow over side of biscuit bowl.)