Mix the butter, sugar and salt in a bowl. Add the eggs one at a time and continue to mix until the mixture turns paler in colour. Combine the flour, baking powder and sodium bicarbonate, stir into the mixture together with the nuts, divide the mixture evenly between 12 muffin cases or greased holes in a muffin tin.
for approx. 20 mins. in the centre of an oven preheated to 180°C. Remove from the oven, allow to cool a little, remove from the tin and leave to cool on a rack.