* halved crosswise (about 3/4 c) In a large skillet, heat the butter and oil over moderately high heat, until the foam subsides. In the fat, brown the chicken on all sides for about 8 minutes, or until it's golden brown. Transfer it with tongs to a plate. Reduce the heat to moderately low and in the fat remaining in the skillet, cook the shallot and garlic for about 3 minutes. Stir in the flour and cook the roux, stirring, for about 2 minutes. Add the Riesling and cook the mixture, stirring, for 1 minute. Add the broth, lemon juice, thyme, and salt/pepper to taste and bring the mixture to a boil, stirring. Return the chicken to the skillet with any juices from the plate and simmer the mixture, covered, for 15 minutes. Add the grapes and simmer the mixture, uncovered, stirring occasionally, for 3 to 5 minutes, or until the chicken is cooked through.