At first, Marty and I were perplexed when a young chef we were talking with in Cuba described a recipe containing an exotic-sounding ingredient called ka-chup. I felt a little silly when it turned out to be good old tomato ketchup. Ketchup is used in quite a few recipes in Cuba, and when combined with bitter orange juice, onion, olive oil, fresh tomatoes, cachucha chiles, and cilantro it makes an easy, refreshing, and distinctly Cuban cocktail sauce for shrimp. Serve this appetizer with casabe, yuca flat bread.