First make the batter. Beat the egg whites until they are stiff; beat the yolks until thick. Sift the flour and salt and baking powder and mix into the egg yolks, then fold in the whites.
Peel the chillies if you wish, but leave the stems on. Slit each one lengthways from tip to stem and remove the pith and seeds. Combine the cheese and onion and carefully stuff the chillies with the mi