Cream the butter and sugar.
Add the eggs one at a time and mix.
Sift in cake flour and baking powder, then mix evenly.
Pour the batter into a pound cake mold.
Mix the crumble topping ingredients (flour, butter, sugar) and sprinkle over the batter.
Bake in a preheated oven at 170°C for 40-45 minutes.
Cool and slice.