Preheat the oven to 180°C. Spray a 23 cm square metal baking tin with cooking spray, then lightly dust with flour, shaking out any excess.
Put the raisins in a small heatproof bowl with the boiling water. Soak for 5 minutes until the raisins are plump and juicy, then drain.
Combine the flour, baking powder, bicarbonate of soda, cinnamon, nutmeg and cloves in a small bowl. Beat the margarine, brown sugar and treacle with an electric mixer in a large bowl until creamy. Add the whole egg and egg white, one at a time, beating well after each addition. Stir in the dry ingredients.
Fold the raisins into the batter. Spread the batter into the prepared tin. Bake for 25 minutes or until the top is springy to the touch and lightly golden. Allow the cake to cool completely in the baking tin on a wire rack, then cut into 24 bars.
Some more ideas…
*Replace half of the raisins with chopped dates. Use 1 cup (160 g) raisins and 1 cup (190 g) chopped dried dates. The dates don't need to be soaked, so reduce the amount of boiling water to 1 cup (250 ml). Add the dates at the same time as the soaked raisins in step 4. *Treacle is a thick, sweet, flavoursome sweetener available in many supermarkets. If you can't find it, try maple syrup instead.
First found in wine, a cholesterol-lowering phyto-chemical called resveratrol is also present in red grapes. Grapes and raisins also supply some potassium and fibre, and are a good source of boron, which helps keep the bones strong.