Preheat oven to 180 degrees C. Lightly grease baking trays, or line with baking paper.
Cream butter with the brown sugar until light and fluffy. Beat in the eggs and mix well. Stir in the salt, cinnamon, nutmeg, cloves, allspice, ginger and flour. Mix to combine. Stir in the oats.
Drop cake mixture onto the prepared baking sheets. Bake for 10 to 12 minutes. Let cakes cool before filling.
Filling: Beat egg white. Mix in the milk, vanilla and 1 cup icing sugar. Beat in the butter and remaining cup of icing sugar. Beat until light.
Tip on sizing
Use an icecream scoop when dropping the cake mixture onto the trays, to achieve same-size results.