Preheat oven to 180 degrees C. Lightly grease one 20cm square cake tin. Line bottom with baking paper or dust lightly with flour.
Sift together the flour, salt, and baking powder.
Cream the butter and blend in the white sugar, eggs and vanilla. Beat until light and fluffy. Add the sifted dry ingredients to the creamed mixture alternately with the milk. Stir until just blended. Pour batter into prepared tin.
Bake at 180 degrees C for 50 to 55 minutes or until cake springs back when lightly touched. Remove from tin and allow it to cool.
Variation: Blueberry Cake
Add 1/4 teaspoon nutmeg to your dry ingredients and stir in 1 cup fresh blueberries into the batter before you bake it. Cut it into squares while it is still hot.