Combine the dough ingredients in the bowl of your stand mixer, and use the dough hook to stir on low till combined then turn the speed up to 6 and knead for 5 minutes.
If the dough feels sticky add another tbsp of flour and knead for another 3-4 minutes at which point if you pick up a piece of dough and stretch it it will be nice and elastic and not break.
Break a small piece off this dough, about golf ball sized, and wrap it around the frozen butter pieces and put them back in the freezer. The dough should stretch in a very thin film around the butter - a too thick dough won't bake through or give you a doughy center.
Leave the remaining dough to rise for an hour in a lightly oiled bowl covered with a kitchen towel inside a draft free space (I put it inside my oven with the oven off).
After an hour give your rise dough a quick turn by hand and divide it into six equal pieces. Flatten each piece out into a circular shape, place the pat of frozen butter inside and form a circle making sure the bottom is well sealed.
Leave them to rise on a lined baking tray for 45 minutes. Gently cover the top with a kitchen towel or a piece of plastic wrap. The dough balls will expand some but this step is important for the texture of the buns!