Meanwhile, in a double boiler, melt the chocolate. Pour it over the cooled pie crust. In a food processor, beat the egg yolks and lime zest until very fluffy, about 5 minutes. Gradually add the condensed milk and continue to beat until thick, 3 or 4 minutes longer. Lower the mixer speed and slowly add the lime juice, mixing just until combined, no longer. Pour the mixture into the crust. Bake for 10 minutes or until the filling has set. Cool on a wire rack, then refrigerate. For the topping: