Sienna restaurant in El Dorado Hills is officially open for business. Just a few minutes ago, owners Mark and Karoline Platt held a ribbon-cutting ceremony, following a soft opening this past weekend. The restaurant is located in the 9,500-square-foot space once occupied by Masque Ristorante. It includes a kitchen that reportedly cost the former owners $1 million to build. Sienna will be open for lunch and dinner seven days a week, serving New American/Asian fusion cuisine. One interesting amenity: a chef’s table for people who want to dine in the kitchen.