Put the cookies in a food processor and blitz to a fine crumb. Add in the melted butter and mix together. Pour into the lined pan and use the back of a spoon to smooth it over and up the sides. Chill while you make the filling.
Put the cream cheese into a large mixing bowl and soften with a wooden spoon. Add the whipping cream and mascarpone, and whisk to soft peaks. Add the cornstarch, then sift in the brown sugar. Whisk together until smooth and firm. Pile the cream filling into the cookie base, then chill for 4 hours or overnight. Top with a generous amount of caramel sauce and chocolate fudge pieces.