In deep fat fryer or heavy saucepan, heat 3 inches oil to 375°F. In another small bowl, mix beer, 1 cup flour and 1 teaspoon mustard. Dip chicken pieces into 1/4 cup flour; coat with beer batter. Fry 5 to 6 chicken pieces at a time, 4 to 5 minutes or until golden brown. Serve hot with aioli.