1.Heat the oven to 200°C/Gas 6 and line a baking tray with baking parchment.
2. Put the flour, salt and bicarbonate of soda into a large bowl and mix well. Add the walnuts and stilton and stir gently. Make a well in the centre of the mixture and pour in half the buttermilk. Using the fingers of one hand (or a rounded-blade knife and then your fingers), draw the flour into the buttermilk. Continue to add the buttermilk until all the flour has been incorporated and you have a sticky dough. You may not need all the buttermilk (different brands of flour absorb slightly more or less liquid).
3. Tip the dough onto a floured surface, shape into a ball and then flatten slightly. Place on the prepared baking tray. Use a large sharp knife to mark the loaf into quarters, cutting deeply into the dough but not quite through the base. Dust the top of the loaf with flour.
4. Bake for 30-35 minutes until the loaf is golden brown and sounds hollow when tapped on the base. You can carefully cut along one of the seams to see if the inside is cooked through; if not, put the loaf back in the oven for 5 minutes or so.
5. Transfer the soda bread to a wire rack and leave to cool completely. It is best eaten on the day it is made, or at least finished within a day or two. It also freezes well.