1. Preheat the oven to 220°C.
2. In a small pot, bring the milk to a gentle simmer. Remove from the heat, add the butter and allow it to melt completely, and then allow the mixture to cool to a lukewarm temperature.
3. In a large bowl, combine 500g flour, salt, caster sugar, yeast, cinnamon, and lemon zest and juice. Create a well and add the cooled milk mixture along with the egg, and bring together using your hand.
4. Turn out onto a lightly floured surface and knead for 10 minutes. Place in an oiled bowl and cover with a damp tea towel. Allow to prove for 40 minutes or until doubled in size.
5. Remove the dough from the bowl and knead in the sultanas.
6. Separate the dough into 12 pieces. Roll into round balls and place neatly into the oiled buffet casserole and allow to prove for another 25 minutes.
7. Combine the remainder of the flour with enough water to form a thick paste. Place in a piping bag and pipe over each dough ball to form a cross.
8. Bake for 25 to 35 minutes or until golden brown. Warm the apricot jam in a small pot, passing it through a sieve to remove any chunks. Remove the buns from the oven and brush with the apricot glaze. Set aside to cool and then break apart to serve.