Ministry of Crab is the most celebrated restaurant in Sri Lanka, opened by cricket legend Mahela Jayawardena and Prasanna Jayawardena in 2011 in the Dutch Hospital complex in the Fort. It specialises in Sri Lankan lagoon crabs — mud crabs caught in Sri Lanka's lagoons — cooked in a menu that ranges from simple garlic butter preparations to elaborate Sri Lankan spiced curries. The crabs are sold by weight; you pick the size (from 500g up to the "Crabzilla" at 2kg+).
The crab with the signature black pepper sauce is the best order. Book well in advance — the restaurant is consistently listed among Asia's 50 Best Restaurants and fills quickly. It's expensive by Sri Lankan standards but inexpensive by international ones.