FOR THE CAKE: – 3 cups (360g) all-purpose flour – 2 teaspoons baking powder – 1 teaspoon baking soda – 1 & 1/2 teaspoons ground cinnamon – 1/2 teaspoon salt – 1 cup (226g) unsalted butter, softened – 1 cup (200g) packed light brown sugar – 2/3 cup (133g) granulated sugar – 4 large egg – 1 tablespoon vanilla extract – 1 cup (226g) sour cream – 2 large pears, cut into small pieces (about 2 cups) – 1 cup (115g) toasted hazelnuts, finely chopped (plus more for garnish) FOR THE GLAZE: – 1 cup (110g) confectioners’ sugar, sifted – 2 to 3 tablespoons sour cream – 1/2 teaspoon vanilla extract