Combine yeast, caster sugar and milk in a large bowl; cover, stand in a warm place for 10 minutes or until frothy. Add egg yolks, butter, the water, flour and salt; stir until combined. Transfer dough to a lightly floured surface; knead for 10 minutes or until smooth and elastic. Place dough in a lightly oiled large bowl; cover, stand in a warm place for 1 hour or until doubled in size.
Process three-quarters of the hazelnuts for 1 minute or until finely ground. Combine ground nuts in a small bowl with demerara sugar and mixed spice.
Preheat oven to 200°C. Grease a large oven tray.
Lightly flour a large piece of baking paper; roll dough out on paper into a 25cm x 45cm rectangle. Lift dough on paper onto tray, cover with plastic wrap; refrigerate for 1 hour or until firmed slightly. (This will assist with shaping the twist.)
Combine 80g (2½ ounces) of extra melted butter with the citrus rinds in a small bowl. Brush butter mixture over dough, leaving a 1cm border; top with ground hazelnut mixture. Firmly roll dough up from one long side, using the baking paper as a guide. Using a sharp knife, cut the roll in half lengthways. Turn the halves, cut-side out on the baking paper, then twist together. Form the twisted lengths into a ring, pressing the two ends together to join.
Transfer the ring, carefully lifting it with the baking paper, onto the oven tray. Brush with remaining extra melted butter; sprinkle with extra demerara sugar.
Bake for 10 minutes. Reduce oven temperature to 180°C; bake for a further 35 minutes or until golden and hollow sounding when tapped. Transfer twist to a wire rack to cool. Serve topped with remaining halved hazelnuts, fig jam and fresh figs.