Melt the butter and crush your crackers into crumbs. Mix together crumbs, butter and sugar. In a 24 cm pie plate, press the dough down with your fingers and form a rim.
Prebake the crust at 175°C for about 10 minutes until lightly browned. Remove from oven and let cool.
Whisk together condensed milk, sour cream, key lime juice and zests. Pour into your pie crust.
Bake again for about 8 minutes. The surface should not brown! (The inside will still quiver when you touch the pan). Chill pie thoroughly before serving.
Whip the cream with an electric mixer until stiff.
Pipe around your Lime Pie (or just add a spoon on every piece when serving) and add some slices of key limes.