Preheat the oven to 190C and line a 20 x 30cm with baking paper
Melt butter, milk chocolate and sugar in a bowl over a pan of simmering water. Leave to cool. Stir in the sugar and 1/2 the chocolate until melted and fully combined.
Beat in eggs, then stir in vanilla. Fold in flour and salt, followed by remaining chocolate. Roughly chop 1/2 the cookies, then stir into mixture.
Spoon the mixture into the baking tin, then top with the remaining jammie dodgers (left whole or halved.) Bake for 25-30 mins, or until risen and golden. Leave to cool in tin before cutting into bars