Serves 8 for the shrimp: 1 lb medium shrimp, peeled and deveined Juice of 1 lemon or lime 2 tsp kosher salt ½ tsp ground peppercorns ½ tsp cayenne pepper for the sauce: ¼ cup water 3 tbls canola oil 12 curry leaves, rightly torn  (optional) 3-6 dried red chiles (optional) 1 ½ tsp cumin seeds ¼ tsp ground peppercorns 2 red onions, chopped 2 tsp kosher salt 1 tbls sugar 1 tbls white wine vinegar 1 ½ cups canned chopped tomatoes 1 tbls unsalted butter 4 slices of bread, preferably brioche, brushed with melted butter, toasted, and halved diagonally.     To prepare the shrimp, place them in a gallon-sized resealable plastic bag. Add the lemon or lime juice, salt, ground peppercorns, and cayenne pepper, shake to coat, and refrigerate while you prepare the sauce.      To make the sauce, place the water next to your stovetop. Heat the canola oil, curry leaves (if using), chiles (if using), cumin seeds, and ground peppercorns in a large saucepan over medium-high heat until the cumin browns, about 2 minutes. Add the onions and salt and cook until they're browned and sticky, 7 to 10 minutes. When the onions start sticking to the bottom of the pan, splash with water and stir and scrape up the browned bits. Stir in the sugar and vinegar and cook for 1 minute. Add the tomatoes and cook until the texture of the sauce is thick and jammy, about 4 minutes. Add the butter and once it has melted, remove the shrimp from the marinade and add them to the saucepan, cooking until they are curled and opaque, 2 to 4 minutes. Place 3 or 4 shrimp on each toast, spoon some sauce over the top, and serve. Courtesy "American Masala," by Suvir Saran, published by Clarkson-Potter, 2007 and used with permission.