Place the biscuits and Walnuts in a food processor and blitz to give fine breadcrumbs, stir in the butter and press into the base and sides of a 23cm fluted flan tin. Bake for 10 minutes and allow to cool.
Meanwhile, whisk the egg yolks until pale and thick, then add the condensed milk, whisk for 2-3 minutes then add the lime zest and juice and whisk for a further 2-3 minutes, stir in ¾ of the Walnuts. Pour into the biscuit base, sprinkle with remaining Walnuts and bake for 20 minutes. Allow to cool before chilling. Serve with lime zest sprinkled on top.
Notes
Cooks tipTop with a little whipped cream to serve.