Preheat the oven to 350 F. Grease a 8 x 8 pan and keep it ready.
In a medium bowl, combine the flour, baking powder, and salt and keep it aside. I usually whisk them together or give it a quick sieve to combine.
In a larger bowl, cream together the butter and the sugar.
Add the egg, vanilla, and milk and beat them well again.
Add the flour mixture in batches and mix gently to combine. The batter will be thicker than the usual cake batter.
Pour the batter into the prepared pan and spread it evenly.
combine the ingredients mentioned for the crumb topping in a small bowl and using a fork mix in the butter with the dry ingredients until they are well combined.
Sprinkle the prepared crumb topping on the batter evenly and press it down gently with a spatula.
Bake for about 25 to 30 minutes or until a toothpick inserted into the center of the cake comes out clean.
Cool in the pan for about 5 minutes and then remove carefully onto a wire rack to cool completely.
Slice and serve with coffee/tea.