Preheat the oven to 350°F.
Grease a 9×9 inch square pan or 9 inch round springform pan. If using a springform pan, line the bottom of the springform pan with a round piece of parchment paper.
In a medium bowl, combine flour, cocoa powder, baking soda, and salt - mix to combine.
Melt the butter and dark chocolate in a small bowl, using a microwave, or on a stove top in a small pan over low heat. Stir well.
Transfer melted chocolate mixture to a large mixing bowl, add granulated sugar, and, using electric mixer, beat on medium-high speed for a couple of minutes until the mixture is light in color. Add eggs and vanilla and continue beating to combine. Add flour mixture and milk, alternating between the two in two additions, into the chocolate mixture.
Pour the cake batter into the baking pan and place chopped pears on top of the cake batter. Alternatively, you can fold in chopped pears into the cake batter before adding the cake batter into the baking pan.
Bake for about 45 minutes or until the toothpick inserted in the center of the cake comes out reasonably clean and the cake bounces when touched.
Cool on a wire rack for 15-30 minutes. If using springform pan, release the cake when completely cooled.
Dust with powdered sugar before serving: it will make this tasty cake look really pretty!