Preparation

1. Sift flour into a large bowl. Add sugar and yeast and stir until combined. Add egg and water and stir until mixture forms a dough. Knead on a floured surface for 3 minutes or until smooth.
2. Gradually knead in butter, 2 cubes at a time. Knead with extra flour to avoid sticking for about 7 minutes or until smooth and elastic. Place in a medium lightly oiled heatproof bowl. Cover with plastic wrap and place in Combo Steam & Convection Oven. Set on convection bake function at lowest temperature 50C, in rack position 1, for 50 minutes until tripled in size.
3. Meanwhile, to make filling, put chocolate and butter in a glass heatproof bowl and heat in the microwave on high for 40 seconds –1 minute. Stir until melted and smooth. Stir in icing sugar and cinnamon until mixture forms a paste. Refrigerate for 15 minutes until firm.
4. Punch down dough. Knead on a lightly floured surface until just smooth. Roll out to a 35cm x 25cm rectangle.  Spread chocolate mixture over dough leaving a 2cm border at one end.  Moisten that end with water. Sprinkle hazelnuts over chocolate. Roll up from short side ending at moist end. Press edges together to seal.
5. Grease and line two sides of a 23cm x 13cm x 6.5cm deep (inner top measurement) loaf pan with baking paper. Cut roll of dough in half down the centre lengthways to expose chocolate layers. Plait two halves together by crossing them over and pressing ends together to join.  Place in loaf pan, tucking under ends.
6. Set aside covered with a plastic wrap in a warm place for 30 minutes until risen just above rim of pan. Bake on inverted wire oven rack in rack position 1 for 20-25 minutes on convection bake setting, covering the top of babka with foil after 7-10 minutes to avoid overbrowning.
7. Meanwhile, to make glaze, put sugar and water in a small saucepan over a medium high heat and stir until sugar dissolves. Bring to a simmer and simmer for 5 minutes. Remove from heat. Pour and brush on top of hot babka. Allow to cool completely. Cut into thick slices and serve with butter.