Melt the butter in a saucepan, add the milk & heat until just warmed through (do not boil or cook for long, only just heat until it is lukewarm). In a small bowl combine the yeast with a 1/2 cup of the warm milk mixture + 1 tsp sugar. Let sit until dissolved & foamy.
In the bowl of a standing mixer fitted with a dough hook, combine the flours, sugar, cinnamon & salt. Add the yeast mixture and remaining milk mixture. Mix on low speed until a dough forms. If it looks too dry & is not fully combining, drizzle in a little more milk until it comes together. Mix on medium speed until the dough is smooth and elastic, 3–5 minutes. If kneading by hand, follow the same process but knead for a little longer. The dough should be soft & very lightly sticky to the touch but not overly so; add a little more flour if needed. The dough is fully kneaded when you slice into it with a sharp knife & see small air bubbles throughout.
Transfer the dough to a clean, lightly oiled bowl, cover with a clean tea towel & let rise in a warm, draught free area for 1 hour, or until doubled in size.