1 Preheat the oven to 160C/Gas Mark 2½. Grease a 450g loaf tin. Sift the flour, baking powder, bicarbonate of soda, spices and salt into a large bowl and mix well.
2 Put the buttermilk or yogurt, honey, oil and egg in a separate bowl and mix until combined. Stir the buttermilk or yogurt mixture into the dry ingredients, then fold in the plums and walnuts.
3 Pour into the prepared loaf tin. The mixture should not fill the tin – leave a gap of about 3cm at the top. Bake for 50-55 minutes or until a wooden pick inserted near the centre comes out clean. Allow to cool a little in the tin before turning out and serve while still warm.