Using a whisk, beat the butter and honey to make a smooth cream, then beat in the eggs one by one.
Add the milk, and whisk again until you have a smooth batter.
Add the flour, poppy seeds, baking powder and a pinch of salt, and mix well.
Add the apple slices, then scrape into a lined or buttered and floured 22 cm baking tin and sprinkle the top with the demerara sugar.
Bake in a 180C (160C fan)/350F/gas mark 4 oven for 40 minutes, or until a skewer or strand of spaghetti comes out clean.
The presence of honey means the cake will brown deeply, maybe before the batter has had a chance to cook though, so keep an eye and, if need be, cover the cake lightly with a foil tent for the last 15 minutes.
