Serve this Scottish classic with plenty of butter. In a large bowl, mix the yeast and caster sugar with 250ml bannock mix water.
Let it stand for 10 mins until the mixture becomes frothy. Tip in the flour and 125g of butter and mix to form a smooth, soft dough. Knead for 5 mins, then put the mixture back in the bowl. Cover with oiled cling film and allow the mix to rise, in a warm place, until doubled in size. Knock back the dough by kneading it lightly for 1 min, then add the sultanas and brown sugar, kneading them in well. Grease a deep 23cm round cake tin with the rest of the butter.
Shape the dough into a round and place in the tin. Allow the dough to rise for 30 mins or until it has doubled in size. Brush the Bannock with a little milk to glaze, then bake for 45-50 mins until risen and browned. The bread should sound hollow when removed from the tin and the base is tapped. If the bread colours too quickly, but is not quite cooked, you can cover it with foil and check after 5 mins more. Cool in the tin for 10 mins, then remove from the tin and finish cooling on a wire rack.