In a large bowl combine the yeast, sugar, 1 teaspoon of the salt and 200g of the flour.
In a saucepan combine the milk, water and 50g of the butter or margarine until 38 degrees C. Add milk mixture and vinegar to the flour mixture and blend at low speed of the mixer until moistened. Beat at medium speed for 3 minutes.
Stir in 200g additional flour to form a sticky dough. Turn dough out onto a floured surface and knead adding more flour until dough is smooth and pliable. Place dough in a greased bowl and let rise in a warm place until doubled in volume.
Punch down dough and roll into a rectangle shape about 40x20cm.
In a saucepan heat the onion, garlic, 1/2 teaspoon salt, parsley and 2 tablespoons butter or margarine until butter or margarine is melted. Spread over the dough rectangle and starting from the 40cm side roll the dough up tightly like a swiss roll.
Place the bread seam side down onto a greased baking tray and let rise until doubled in sized.
Preheat oven to 200 C / Gas 6.
Bake bread until golden brown about 20 to 30 minutes. Brush hot bread with melted butter and sprinkle with chopped parsley.