Line a Swiss roll pan with oiled
greaseproof paper. Pre-heat oven to hot 200C (400F). Boil leeks in water for 3 minutes. Drain well., mix egg yolks with half
the cheese. Stir in leeks and chives. Beat egg whites until stiff peaks
form. Fold whites into leek mixture. Spread mixture evenly over greaseproof
paper. Bake for 15 minutes until firm. While roulade is cooking, sauté bacon
in butter until browned. Add mushrooms, cook 2 minutes, stir in
mustard. When cooked, turn roulade out onto a
clean, soft tea towel. Remove greaseproof paper, spread bacon
mixture over the top. Sprinkle with remaining cheese, roll
up as for a Swiss roll. Serve sliced with salad.