In food processor, grind half of the hazelnuts to slightly coarse texture (a little coarser than coarse salt). Using back of knife, break remaining nuts into large chunks. Grate the rind from the oranges; juice 1 orange. Set aside.

In bowl and using mixer, beat yolks, granulated sugar and salt until creamy and very light in colour, about 5 minutes. Beat in grated orange rind and 1 tbsp (15 mL) of the orange juice; beat in butter. Mix in candied rind. In bowl, whisk together flour and baking powder. Mix into egg mixture just until well incorporated. Form dough into two 1-1/2-inch (4 cm) logs. Spread ground nuts on work surface. Roll dough in nuts to coat entirely. Wrap in waxed paper and refrigerate for at least 2 hours or up to 1 day.

Slice dough into 1/4-inch (5 mm) thick slices. Place on parchment paper–lined baking sheet. Bake in top and bottom thirds of 350F (180C) convection oven or 375F (190C) conventional oven, rotating and switching pans halfway through, until golden-brown, 10 to 12 minutes. Transfer to rack. In small bowl, mix icing sugar with 2 tbsp (30 mL) of the orange juice to make a thick glaze, adding more juice if necessary. With small spatula, spread glaze over warm cookies and top with 2 or 3 hazelnut chunks. Let cool. (Make-ahead: Store in covered container at room temperature for up to 2 weeks.)

Makes about 6 dozen cookies.