Preheat oven to 160?C/140°C fan forced.

In a large pot, combine the butter, sugar and cream, and bring to a boil. Simmer until the mixture reaches 115?C on a candy thermometer or soft-ball stage. (Test this by dropping a small amount of the mixture into a cup of chilled water ? it should form a firm but flexible ball.) Add half of the pistachios and mix gently.

Place a spoonful of the mixture onto well-greased baking paper. Dip the spoon into water and flatten the mixture out with the back of the spoon to form a very thin disc. Repeat until all the mixture has been shaped, allowing adequate space for the florentines to spread while they bake. Sprinkle the tops with the remaining pistachios and the orange zest.

Place in the oven near the top shelf and bake for 15 to 18 minutes or until the florentines bubble and turn golden. Remove from the oven and immediately cut into precise rounds using an 8cm circular cookie cutter. Allow to cool before removing from the baking paper.

Cook's Notes:Lightly toast the crushed pistachios and season lightly with salt before mixing into the sugar for a more complex flavour.