Swap the trout for hot-smoked salmon,
or a mixture of prawns with some
snipped smoked salmon trimmings.
Heat oven to 200C/180C fan/gas 6.
Melt the butter in a saucepan, then stir
in the flour for 1 min. Gradually stir in the
milk and horseradish, if using. Bubble
the sauce to thicken for a couple of mins,
then add the dill, three-quarters of the onions, the lemon zest, fish and some
seasoning. Pour into 4 individual pie
dishes or 1 large pie dish.
Mix the mashed potato with the
remaining spring onion. Spoon over the
fish mixture, then bake for 15-20 mins
until golden and bubbling.