Combine milk and butter in a small saucepan over low heat. Warm for 2 mins or until butter melts. Set aside to cool slightly.
Combine flour, sugar, spices and sultanas in a large mixing bowl.
Add the yeast to the warm milk mixture and whisk to combine. Let sit for a minute until the yeast starts to form bubbles.
Lightly whisk the egg then add to the dry ingredients along with the milk mixture and stir until well combined. Turn onto a lightly floured surface and knead for 8-10 mins or until dough is smooth and elastic. If you have a stand mixer, you can knead using a dough hook for about 5 mins on low speed. Transfer to a very lightly oiled bowl and cover with cling wrap. Place in a warm, draught-free place for 1 hour or until dough doubles in size.
Line a medium oven tray with baking paper. Punch down the dough. Turn onto a lightly floured surface and knead until smooth. Divide the dough into 12 even portions and roll each portion into a uniform ball (about 115g each). Arrange side-by-side in lined pan and press down lightly on each ball. Loosely cover with plastic wrap and place in a warm, draught-free place for 30 mins to rise.
Preheat oven to 200°C. To make the flour paste, place flour in small jug. Stir in enough water to make a smooth, thick paste. Place in a resealable snack bag and cut off 1 corner to create a 3-4mm opening. Pipe the paste over the buns to make crosses.
Bake for 10 mins then reduce oven to 180°C. Bake for a further 12-15 mins or until golden brown and the buns sound hollow when tapped on the base. Immediately transfer to a wire rack and set aside for 10 mins to cool slightly.
To make the glaze, combine the sugar, gelatine and water in a small saucepan over low heat. Cook for 1-2 mins or until the sugar and gelatine dissolve. Brush over the buns. Serve warm with lashings of butter.