Cook the peas briefly in boiling water, then drain them.
Finely grate the parmesan.
Break the eggs into a bowl and lightly mix them, stir in the smoked haddock, half the parmesan and peas.
Heat the grill.
Melt the butter in a shallow non-stick 24cm frying pan. When the butter starts to froth, pour in the egg mixture. Let it cook over a relatively low temperature until the bottom has formed a golden crust. The centre will probably still be wobbly. Lift the pan from the heat and put it under the grill until the eggs have set and the top is lightly coloured.
Turn out onto a plate and cut into wedges like a cake.
Top tip: Combine eggs with other ingredients in a bowl, not the pan – don't stir the frittata.