Preheat the oven to Gas Mark 4, 180°C, fan 160°C. Grease and line a 20cm (8in) round baking tin with nonstick baking paper.
First make the topping: melt the butter and stir in the muesli, mix well and reserve.
In a frying pan heat 25g (1oz) of butter, honey, 1tbsp of sugar and the apples. Cook until the apples are soft and golden. Set aside.
In a bowl beat the remaining butter and sugar until pale and fluffy. Add the eggs gradually, beating well between each addition. Then carefully sift in the flour and baking powder, and mix in. Add the crème fraîche and mix until smooth. Spoon about half the mixture into the greased cake tin. Add half the topping mix. Cover with the rest of the cake mixture. Place the cooked apple on top and cover with the rest of the topping.
Bake for about 45 minutes. If the cake looks like it is browning too much then loosely cover with foil or baking paper to protect the cake. The cake is cooked when a skewer inserted into the cake comes out clean.
Allow to cool in the tin for 10 minutes before removing.
*Inspired by Kate H. featured in the Reafood Cookbook