Step by step

Make a béchamel substituting half the milk with fish stock, then spread a first layer of this sauce on the base of an oven dish, then add a layer of homemade lasagne

You can keep lasagna in the fridge in an airtight container for 2-3 days at most.
Although lasagna has known its greatest fame and has spread across the world since World War II onwards, in ancient Rome there was a similar dish. And we read in ‘The culinary art of Apicius’ that lasagna was the favourite dish of Cicero.