Preheat the oven to 180 C / Gas 4. Grease a 900g loaf tin and line with baking parchment.
For the topping:
Prepare the top of the cake by melting the caster sugar in a frying pan over a low heat. Add the orange slices and cook on both sides for 6 to 8 minutes until they are caramelised and golden. Remove from the heat and set aside.
For the cake:
Cream the butter and sugar together until light and fluffy. Add the eggs, orange juice and milk and beat well. Fold in the flour together with the baking powder, spices and zest. Spoon into the prepared loaf tin and smooth the top. Add the three orange slices and push into the mixture just slightly.
Bake in the preheated oven for 60 to 90 minutes until a skewer inserted into the centre comes out clean. Remove from the oven and allow to cool before slicing and serving.