Prepare the milk mixture: Heat milk and set aside two tablespoons to cool to 38°C. Melt butter into the remaining milk.
Activate yeast: Dissolve yeast and sugar in the cooled milk and let it sit for 5 minutes.
Combine dry and wet ingredients: Mix flour and salt. Beat an egg and add it to the flour. Gradually add the yeast mixture and the remaining milk and butter mixture to form a soft, slightly tacky dough.
Knead and first prove: Knead for about 10 minutes until smooth and elastic. Place the dough in a lightly oiled bowl, cover with oiled cling film, and let it rise in a warm place until doubled in size (about 1 hour).
Second prove: Knock back the dough, shape into a loaf, and place it in a lightly oiled bread tin. Cover with oiled cling film and let it rise until at least half its size again (about 30-45 minutes). To check if the dough is sufficiently proved, lightly press it; a small indentation should remain if it's ready.
Bake: Preheat oven to 200°C (gas mark 6). Bake for 25-30 minutes, until golden brown and the bottom sounds hollow when tapped.