Overnight Chelsea Buns

Mix the dough. Put the flour into a large bowl with the yeast and the caster sugar on one side and the salt on the other, and grate in the orange zest. Warm the milk until it is barely above blood temperature, so it feels neutral rather than warm on the inside of your wrist, then whisk the whole egg and the extra yolk into it. Pour that into the flour and mix to a rough, shaggy dough, then work in the softened butter a little at a time until it disappears.

Knead until it is properly elastic. Knead for about 10 minutes by hand, or 6 to 8 in a mixer with a dough hook. Enriched dough is slack and sticky at first and firms up as the gluten builds, so resist adding flour. It is ready when you can stretch a piece thin enough to see light through it without it tearing.

First prove. Cover the bowl and leave it somewhere warm until doubled, usually 1 to 1.5 hours. Go by size rather than the clock: butter, milk and egg all slow a dough down, so this takes longer than a plain loaf, and longer again in a cold kitchen.

Make the filling. Beat the very soft butter with the light brown sugar and the mixed spice into a spreadable paste. It wants to be soft enough to spread without dragging the dough about.

Roll it out and fill it. Knock the dough back and roll it into a rectangle roughly 30 by 40 cm, with a long side towards you. Spread the filling over it, leaving a clear 2 cm strip along the far long edge, then scatter over the sultanas or currants and press them lightly in.

Roll up and cut into 15. Roll it up firmly and evenly from the long edge nearest you, without stretching the dough as you go. Pinch the bare strip along the seam to seal it, trim the ragged ends, and cut the roll into 15 slices.

Into the tin, then into the fridge. Line a 20 by 30 cm tin with baking parchment and set the slices in it cut side up, leaving a small gap around each one. They will expand into those gaps overnight and finish joining in the oven. Cover the tin and put it in the fridge for 8 to 12 hours.

The next morning, let them wake up. Take the tin out and leave it at room temperature for 1 to 2 hours, until the buns look puffy and have risen enough to touch one another. Do not bake them straight from the fridge.

Bake. Heat the oven to 190C, 170C fan. Bake for 22 to 25 minutes, until deep golden. If the tops or the exposed fruit are colouring too fast, lay a sheet of foil loosely over the tin. A bun from the middle of the tray should read 85C inside.

Glaze while they are hot, then cool. While they bake, bring the caster sugar and the water to the boil and let it bubble for a minute. Brush it over the buns the moment they come out, while they are hot enough to drink it in. Leave them in the tin for 10 minutes, then lift the parchment out and cool them on a rack.