Heat the oven to 180°C (160°C in a fan oven), 375°F, gas 5 and grease the ramekins with the butter and sprinkle with the sugar.
Mix together the milk, cocoa, orange zest and 25 g sugar. Place in a pot and bring to the boil. Remove from the heat and take out the orange zest. Add the chocolate and allow to melt.
Beat the egg white with a pinch of salt until stiff and gradually mix in the remaining sugar. Stir the egg yolks and flour into the melted chocolate. Fold in the beaten egg whites and transfer the mixture to the prepared ramekins.
Place a pear in each ramekin and place the ramekins into a large, oven-proof dish. Fill the dish with 2-3 cm of hot water and transfer to the oven. Bake for 25-30 min. Remove from the oven and serve immediately.