To make the batter for the fish, dissolve the yeast in 3 tbsp of the milk and leave in a warm place for 10 minutes. Combine the remaining ingredients in a bowl and beat until smooth, then add the yeast and some salt. Cover and leave to ferment for 1½-2 hours. If the batter is too thick, add a little water.
To make the pea purée, heat the butter in a pan and gen