Preheat the oven to 160 C / Gas 3. Grease a 20cm cake tin
In a food processor, purée one of the pears and transfer to a bowl. Mix in the flour, baking powder, milk, water, sugar, honey, cinnamon and ginger. Mix well. Chop two of the remaining three pears and mix into the cake mixture.
Whisk the egg whites until stiff peaks form then fold into the cake mixture.
Slice the remaining pear and arrange on the bottom of the prepared cake tin. Pour over the cake mixture.
Bake for 60 to 80 minutes until a skewer inserted in the centre comes out clean. Remove from the oven and allow to cool before serving.