Preheat oven to 175°C (350F) and grease a 9" round springform cake tin with butter or line it with parchment paper.
Sift and mix flour, cocoa, baking powder, salt, and cinnamon and set aside.
Place butter and sugar in a large bowl of a stand mixed fitted with the paddle attachment. Mix on medium speed for 1-2 minutes until pale and fluffy.
Add vanilla extract and eggs, one by one, mixing well after each addition.
Add dry ingredients in two additions, alternating with milk and mix until just combined. Do not overmix.
Pour cake batter into prepare cake tin.
Wash and core pears and thinly slice them. Press pear slices into cake batter, in a circular pattern.
Bake cake for 45-55 minutes or until a toothpick inserted into the center comes out clean.
Allow cake to cool for 10 minutes in cake tin, then transfer to a cooling rack to continue cooling. Sprinkle with powdered sugar, slice, and serve.