Grease and line with greaseproof paper a 20cm (8 in) square tin. Preheat the oven to 170 C / gas 3.
Put the flour and sugar into a bowl and rub in 175g of butter, clumping the dough together to make a ball. Press this sandy shortbread mixture into the tin and smooth it down.
Prick with a fork and cook for five minutes, then lower the oven to 150 C / gas mark 2, and cook for a further 30-40 minutes until pale golden and no longer doughy. Allow to cool in the tin.
Melt the remaining 200g of butter in a large microwavable bowl, then add condensed milk and golden syrup. Whisk the mixture well until the butter is thoroughly incorporated. Heat in microwave for 6-7 minutes until boiling, stirring thoroughly every minute. It's ready when it's thickened and turned a light golden brown. Pour this molten toffee over the shortbread and leave to set.
Melt chocolate and pour over the caramel mixture and leave to cool. Once set, cut the millionaire's shortbread into pieces.
I followed this recipe to the letter and I had a problem with the caramel. I found the microwave technique of cooking it awkward as it went from barely tepid to suddelny boiling all over my microwave. I don't know if this recipe requires that the caramel is allowed to boil for a while but using the microwave method it is impossible and only boils for a second before making a huge mess. Anyway, I am assuming it is this that caused the caramel then not to set. So, the result: The biscuit was perfect. The caramel was very sloppy. the chocolate was a little thick and needed a huge whack with a big knife to cut through it (which resulted in uneven "slices" and also made the caramel squidge out the sides even more). It did taste gorgeous but it was a knife and fork job and on day two was eaten with custard, which was delicious. But certainly did not look like the picture!
What should be done to make the caramel firm!?? - 22 Mar 2010