Preheat the oven to 180C/160C Fan/Gas 5. Line an 8" square baking tin.
In a food processor, or using the end of a rolling pin, crush the biscuits and cornflakes to a fine crumbly texture (think of wet sand). Stir in the melted butter and press into the tin. Bake 10 minutes.
Make the caramel: In a medium saucepan, combine the caramel, Biscoff spread, butter and sugar. Heat on a medium heat (it should be bubbling, but not too high), for 5 minutes, stirring constantly. Pour over the biscuit base and chill 30 minutes.
Melt the white chocolate breaking up the chocolate into a small bowl and microwaving in 20 second intervals, stirring in between, to prevent it from burning. Pour over the caramel layer. Add any biscuits/stir in some Biscoff spread to decorate. Let set 1h30m.
Slice, before returning to the freezer for a few minutes to serve!