Preheat oven to 350°F (175°C). Grease a 20cm square pan.

In a large bowl, combine brown sugar, flour, baking powder, baking soda, and salt.

Rub butter into the dry ingredients until the mixture resembles fine breadcrumbs.

Press half of the mixture into the prepared pan to form a base.

Dissolve baking soda in lowfat milk.

Add beaten egg and nutmeg to the milk mixture.

Pour the milk mixture over the remaining sugar and flour mixture.

Mix well to combine.

Spoon the batter over the pressed base in the pan.

Sprinkle minced walnuts evenly over the top.

Bake in the preheated oven for 1 hour, or until a wooden skewer inserted into the center comes out clean.

Let the cake stand for 15 minutes before turning it out onto a wire rack to cool completely.