Preheat the oven to 180℃ (160℃ fan)/350°F/gas mark 4. Grease and line a rectangular baking tin about 23 x 27cm( 9 x 11 in).
Beat the butter and sugar together until light and fluffy. Add the eggs one at a time beating well after each addition.
Beat in the cinnamon, then add the apples and mix well.
Gently fold in the flour until well combined. Spoon into the prepared tin and spread level. Sprinkle over the demerara sugar if using
Bake in the centre of the oven for 45 minutes, until risen and golden. The cake will spring back when gently pressed in the centre with your finger.
Allow to cool in the tin. Transfer to a board and cut into squares to serve.
Video
Notes
The cake freezes well for up to 3 months.Nutrition information is approximate and is meant as a guideline only. (It does not include the optional demerara sugar.)