Grease and line a 30 x 23 cm (12 x 9 inch) roasting tin with nonstick baking paper, snipping diagonally into the corners so it lines the base and sides. Place the nuts on a piece of foil and toast under the grill for 3–4 minutes until golden. Roughly chop 2 tablespoons and reserve for decoration, then finely chop the remainder.
Whisk the yolks and sugar until they are thick and pale and the whisk leaves a trail. Fold in the finely chopped hazelnuts and pear. Whisk the whites into stiff, moist-looking peaks. Fold a large spoonful into the nut mix to loosen it, then gently fold in the remaining egg whites.
Spoon the mixture into the prepared tin. Bake the roulade in a preheated oven, 180°C (350°F), Gas Mark 4, for 15 minutes until golden brown and the top feels spongy. Cover and leave to cool for at least 1 hour.
Beat the mascarpone and icing sugar together until soft. On a work surface, cover a damp tea towel with baking paper and sprinkle with sugar. Turn the roulade on to the paper and remove the tin and lining paper.
Spread the roulade with the mascarpone mixture, then with the apricots. Roll up the roulade, starting from the short end nearest you, using the paper and tea towel to help. Transfer the roulade to a serving plate, sprinkle over the reserved hazelnuts and cut into thick slices.