Sieve flour with baking powder and salt and set aside.
Cream together butter and 200g sugar until light. Beat in egg and vanilla until fluffy. Add flour mix alternately with milk, beginning and ending with the flour mix.
Spread the cake mixture into a greased 18x28cm or similar sized baking tin. Gently press apple wedges into cake. Sprinkle with 4 tablespoons sugar and cinnamon.
Bake at 180 C / Gas 4 for 50 to 60 minutes or until apples are tender and cake is golden brown.
Leave to cool for 5 minutes, then serve warm with vanilla ice-cream or hot custard.