For the flavourings, crumble the Stilton into a bowl and add the walnuts. Stir in the sultanas and set aside.
For the soda bread, preheat oven to 200C/180C Fan/Gas 6. Line a baking tray with parchment paper.
Tip the flours, bicarbonate of soda and salt into a bowl. Add the flavourings.
Pour in the buttermilk and mix to a soft dough. Tip out onto a floured surface and gather into a ball. Cut deep slits in the loaf to mark out quarters and dust with flour.
Place the bread on the baking tray and bake for 30 minutes, or until golden-brown and cooked through. The loaf should sound hollow when tapped on the base.
Remove from the oven and cool on a wire rack.