Why This Recipe Works
Millionaire’s shortbread has a lot going for it: a crunchy shortbread base; a chewy, caramel-like filling; and a shiny, snappy chocolate top. The only thing that could make it better would be foolproof methods for producing all three layers. We started by making a quick shortbread with melted butter rather than pulling out the mixer or food processor. Sweetened condensed milk is important to the flavor of the filling, but it also makes the filling vulnerable to breaking because the whey proteins, crucial to keeping the mixture emulsified, have been damaged by heat both during processing and during the cooking of the filling. We added fresh cream to supply just enough whey to keep it together. Melting the chocolate very carefully so that it never got too hot and stirring in grated chocolate at the end created a smooth, firm top layer, which made a suitably elegant finish for this rich yet refined cookie.