1.Grease a deep 23cm square cake pan, line base with paper; grease paper.
2.Cream butter and sugar in small bowl with electric mixer until light and fluffy. Beat in eggs one at a time, beat until combined. Transfer mixture to large bowl, stir in half the sifted flours and soda and half the buttermilk, then stir in remaining flours and buttermilk. Spread into prepared pan, sprinkle with cinamon topping. Bake in moderate oven for about 50 minutes. Stand 5 minutes before turning on to wire rack to cool.
3.To make Cinnamon Topping, Cream butter and sugar in small bowl with electric mixer until light and fluffy. Stir in sifted flour and cinnamon. Push mixture through coarse sieve.