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 and slowly pour into the well of dried ingredients. 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.