Whisk the flours into the milk and add the salt. Beat in the eggs one at a time. Whisk the mixture until it is smooth and let it rest for half an hour. Heat a frying pan and add the butter. Pour the batter into the centre of the pan so that it spreads out to form a thin, lace-like layer. Once the underside of the pancake has cooked, fry the other side until it is a lovely golden colour then place on a preheated plate and cover with a lid. Continue until you use up all the batter. Serve with strawberry jam or whipped cream.