Preheat the oven to 190 ° C and grease the muffin tray well. Wash, peel and cut the pears into small pieces. Chop the chocolate into small pieces. Mix the flour, baking powder, baking soda, hazelnuts and chocolate in a bowl. In a second bowl, beat the eggs, sugar, oil, Nutella and yoghurt until frothy. Add flour mixture and pear pieces and stir in. Pour the batter into the molds and bake for about 20-25 minutes.