Preheat the oven to 180 C (160 C fan). Put the leftover cake into a food processor and blitz to fine crumbs. Pour in the melted butter and pulse a few times until it’s well mixed together. Pour the crumb into a springform tin use a glass or the back of a spoon to smooth it over, pressing it down firmly. Use a knife to shape the edge as best you can, then chill for 30 minutes. Once it’s chilled, gently warm the jam in a saucepan to loosen it up, then carefully spread it over the base of the crust, and put to one side.
In a large saucepan, warm the butter, sugar and syrup, stirring until the sugar has dissolved. Tip in the cornflakes and stir it well to make sure they’re all covered, then tip it into the the crust and spread it around. Put the pie into the hot oven for 15 minutes, then leave it to cool completely in its tin before removing it and cutting into slices to serve.
