Complex sentence: After returning to America, Robert often stayed at weekends with his beloved French grandmother in upstate New York, and she taught him to cook, making biscuits and butter-frying fish caught in a nearby stream.
Split into simpler sentences: After returning to America, Robert often stayed at weekends with his beloved French grandmother in upstate New York. She taught him to cook, making biscuits and butter-frying fish caught in a nearby stream.