Claire Ptak is an American pastry chef who moved to London in 2005 after working at Chez Panisse restaurant in Berkeley, California. She owns Violet, a baking company in East London. Her popular stall in Broadway Market is best known for its American-style cupcakes with seasonal buttercream frostings. She recently opened a café and cake shop nearby, where whoopie pies have become a much-loved fixture. www.violetcakes.com.