Peel and chop the potatoes into thick chips, then coss with the olive oil and some salt. Arrange on a large non-stick baking tray and roast for 20 mins, turning halfway.
Lightly toast the bread, then pulse briefly in a food processor for coarse breadcrumbs. Dust the fish in flour, shaking off the excess, then dip into the egg, then breadcrumbs to coat thoroughly. Roast the fish with the chips for a further 20 mins, until both are golden.
Just before the fish and chips are ready, boil the peas for 3-4 mins, then drain and mash. Stir in the crème fraiche or a knob of butter and season with salt pepper or herbs.