Key limes are smaller, yellower cousins to the bigger, darker green Persian limes you usually see in the grocery store. They’re more tart, with fragrant, floral juice, and used to be grown widely in the Florida Keys, where cooks invented key lime pie as a way to use the juice. To make these key lime bars, you don’t actually need key limes. They can be hard to find and are so small that you’d have to squeeze 20 of them to get 1/3 cup of juice! Regular Persian limes work just fine; but whatever you do, don’t use bottled lime juice in this recipe (fresh juice has much better flavor!). Then there’s toasted coconut. It’s a great addition to baked goods such as cookies or bars, or as a topping for ice cream or oatmeal. It can sometimes burn when you toast it in the oven, so we like to …