Apple cake with crunchy topping

This apple cake is really delicious. Everybody has their favorite apple cake, this is mine. Recipe from The hummingbird bakery in London.

Apple cake with crunchy topping
1/4 cup (2 oz) softened butter
5 oz all-purpose flour
3 1/2 oz granualted sugar
1 large egg
1/2 tsp vanilla extract
1 tsp baking powder
1/8 tsp salt
1/3 cup milk
3 Granny smith apples

Crunchy topping
2 1/2 oz all-purpose flour
1/2 tsp ground cinnamon
1 1/2 oz cold butter, diced
2 1/2 oz soft light brown sugar

Preheat oven to 325 F. Grease a round baking tin (about 8 X 2 inch)
First make the crunchy topping.
Sift flour and cinnamon into a baking bowl. Add the butter and using your fingertips
rub the ingredients together until they resemble breadcrumbs. Stir in the sugar and set aside.
Then peel,core and thinley slice the apples. 

Using a handheld electric whisk or a kitchen aid with paddle attachment,cream butter and sugar
until pale and fluffy. Add egg and vanilla and beat well on medium speed.
Sift together flour, baking powder and salt. Add half to the butter/egg mixture followed by half the milk.
Mix well on medium speed after each addition and repeat with the rest of the flour and milk.
Pour batter into the tin.
Arrange the sliced apples into circles on top of the batter. Sprinkle over the crunchy topping.
Bake for 30-40 minutes until the topping is golden brown. If using a skewer, it should come out clean.
Set aside to cool in the tin. Serve as is or with whipped cream.