Preheat oven to 180 degrees C. Grease and flour a 25cm cake tin and line the bottom with baking paper.
Cut the vanilla bean in half and place with the milk in a small saucepan. Bring to a simmer, remove from heat, cover and let cool. Remove the seeds from the bean and stir into the milk.
In a bowl, sift together the flour and baking powder. Place the cocoa in a cup and stir in the two tablespoons boiling water. Cut the pears into 4 segments each and sprinkle with lemon juice to prevent browning.
Beat butter with sugar until light. Beat in eggs one at a time, then add salt, cocoa and milk. Mix well. Add the flour and baking powder. Mix quickly until just combined.
Pour the batter into the cake tin and decorate the top with the slices of pear.
In a saucepan, combine butter, sugar and cinnamon and brush over the pears. Bake 1 hour.
Remove from the oven, let rest 10 minutes then cool on a wire rack.