1.Preheat oven to 200°C (180°C fan-forced). Oil a six-hole 180ml texas muffin pan and line each hole with two criss-crossed 5cm x 20cm strips of baking paper.
2.Using a sharp knife, V-slicer or mandoline, cut potatoes and onion into very thin slices. Drain and reserve oil from anchovy fillets in oil (you need 2 tsp of the oil) and chop anchovies coarsely. Layer potato, onion and anchovy in pan holes, starting and finishing with potato.
3.Heat reserved anchovy oil, cream and milk in a small saucepan. Pour hot cream mixture over potato mixture. Bake 35 minutes or until potato is tender. Stand in pan 10 minutes.
4.Using baking-paper strips as lifters, remove gratin from pan holes. Serve gratin sprinkled with dill.