Boil the potatoes for 15-20 mins until tender, then drain.

Reserve 3 tbsp corn and blitz the rest (with its juice) using a hand blender or a food processor until completely smooth, then mash into the potatoes.

Cook the spinach following pack instructions – if you have a microwave, choose this method.


2)Put the leeks in a pan with the 300ml milk and the butter.

Cook gently, part-covered, for 8 mins until the leeks are tender.

(Keep an eye on things as milk can easily boil over.)

Mix the 3 tbsp milk with the flour and mustard, then stir into the leek mixture – keep stirring until thickened.

Take off the heat and stir in three-quarters of the cheese.

3)Squeeze as much liquid as you can from the spinach, then arrange on the base of 2 gratin dishes.

Place a fish fillet on top of each, then spoon over the leek & cheese sauce.

Top with the sweetcorn mash