Sieve the white flour and bicarbonate of soda and salt into a large mixing bowl, and stir in the wholemeal flour. Using clean hands mix the flours, bread soda and finely chopped fresh rosemary together. Make a well in the centre of the bowl.
Whisk together the yogurt and milk to form buttermilk, and slowly pour into the well of dried ingredients. Reserve a small amount for a wash in step five. Using your free hand to mix the flour into the buttermilk, try and spread your fingers far apart so it resembles a trough. Make sure that there are no dry patches and that the dough is completely wet.
Pat your hands with flour and shape the dough into one round. Place on a floured baking tray. Flour a large knife and cut the shape of a cross into the top of the dough about two-thirds of the way through.
Brush the round of bread with the milk and yogurt mixture using a pastry brush, this will give a lovely golden colour to the bread once baked
Bake in a pre-heated oven at 425 degrees Fahrenheit for 25 minutes, then reduce the heat to 350 degrees Fahrenheit for a further 25 minutes. To test whether the loaf is cooked, tap the back with your knuckles; it should sound hollow. Leave to cool on a cooling rack.