Activate the Yeast: In a small bowl or jug, gently warm the milk until it's lukewarm. Stir in the yeast and 1 teaspoon of the caster sugar. Set it aside for 5-10 minutes until it becomes frothy and bubbly on top. This shows the yeast is active and ready to go. If it doesn't froth, your yeast may be old, and it's best to start again.

Make the Dough: In the bowl of a stand mixer fitted with a dough hook, combine the bread flour, the remaining caster sugar, and the salt. Give it a quick mix. Pour in the frothy yeast mixture and the egg. Mix on a low speed for about 2 minutes until a shaggy dough begins to form.

Knead the Dough: Add the softened butter, one cube at a time, mixing well after each addition. Once all the butter is incorporated, increase the mixer speed to medium-low and knead for 8-10 minutes. The dough should become smooth, elastic, and pull away from the sides of the bowl. To check if it's ready, you can do the 'windowpane test' explained by experts at King Arthur Baking. If kneading by hand, tip the dough onto a lightly floured surface and knead for 10-15 minutes.

First Proof: Shape the dough into a ball and place it in a lightly oiled bowl. Cover with cling film or a damp tea towel and leave it in a warm, draught-free place for 1 to 1.5 hours, or until it has doubled in size.

Prepare the Filling and Shape the Loaf: While the dough is proving, mix the soft butter, dark brown sugar, and cinnamon together in a small bowl to form a paste. Once the dough has risen, gently punch it down and tip it onto a lightly floured surface. Roll it out into a rectangle approximately 30cm x 40cm. Spread the cinnamon filling evenly over the dough, leaving a small 1cm border along one of the long edges.

Roll and Second Proof: Starting from the long edge opposite the clean border, roll the dough up into a tight log. Pinch the seam to seal it securely. Place the log, seam-side down, into a greased and lined 900g (2lb) loaf tin. Cover again and leave to prove in a warm place for another 45-60 minutes, or until it has risen to just above the rim of the tin.

Bake the Bread: Towards the end of the second proof, preheat your oven to 180°C (160°C fan). Bake the loaf for 30-35 minutes, until it's a deep golden brown and sounds hollow when tapped on the bottom. I find that covering it loosely with foil for the last 10 minutes prevents the top from getting too dark.

Cool and Ice: Let the bread cool in the tin for 10 minutes before carefully turning it out onto a wire rack to cool completely. If you're adding icing, whisk together the sifted icing sugar, vanilla, and 1 tablespoon of milk until smooth. Add more milk, a drop at a time, until you reach a thick but pourable consistency. Drizzle it over the completely cooled loaf.