Line the base of an 8-inch round non-stick springform pan with parchment paper. Butter the paper and sprinkle a tablespoon of raw sugar over it. Arrange the sliced pears in a circle (or something like it) around the base.

Preheat oven to 350 degrees F.

Melt chocolate with butter and salt in a small saucepan over very low heat and set aside to cool slightly.

In a large bowl, beat the egg yolks with half of the sugar until very pale and thick and nearly tripled in volume. This will take 3-5 minutes on high speed. Fold in ground hazelnuts and vanilla extract. Stir through the cooled melted chocolate mixture and set aside.

In a separate large bowl, beat the egg whites with remaining sugar with an electric mixer on medium speed until very stiff and glossy. Gently fold it into the chocolate mixture.

Pour the batter evenly over pears in the prepared pan and bake for 45-50 minutes, or until puffed and slightly cracked at the surface. A skewer inserted into the center will come out with some moist crumbs. Transfer pan to a wire rack to cool completely before serving.