Preheat oven to 400°F.
Grease a popover pan or muffin tin.
In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
In a separate bowl, whisk together the sugar, eggs, oil, milk, and vanilla.
Fold the wet ingredients into the dry ingredients until just combined.
Peel, core, and dice the pears.
Fold the pears and chopped hazelnuts into the batter.
Scoop the batter into the prepared pan, filling each cup about ¾ full.
Bake for 18-20 minutes, until a toothpick inserted in the center comes out clean.
Allow to cool in the pan for 5 minutes before transferring to a wire rack.
