A "healthy" potato bake

A former housemate of mine loves a potato bake.  One afternoon he cooked one and the two of us sat on his bed and ate the whole thing.  Delicious.  Definitely not healthy - think of all the butter and cream (he is a bean pole, so that didn't bother him). 

Instead, I decided to give this version a try, a supposedly healthier version, despite the cubes of butter you put on top at the end.

Layers of parcooked potatoes, ricotta, spinach and tinned salmon.  With a fairly small amount of cheese and butter on top.