Place the warm water, milk, yeast and sugar in a jug, give it a stir and leave for 5 minutes until the top of the liquid starts to foam slightly. If it doesn't foam then your yeast isn't active and you'll need to start again with a new packet of yeast.
Place the two flours, the butter and salt into a mixer and mix together using the beater attachment for a minute - until you can no longer see lumps of butter.
Add in the water/yeast mixture and one of the eggs, then beat again (using the beater attachment) for 10 minutes on medium speed. The dough will be sticky, but will come together in a soft, slightly sticky ball towards the end.
Place the dough in a large bowl and cover with clingfilm. Leave to rise in a warm room until doubled in sized (usually 1-2 hours).
Line a large baking tray with baking parchment or a silicone mat.
Once the dough has doubled in sized, tip it out onto a floured (plain /all-purpose flour) surface and punch the air out of it. Cut the dough as evenly as you can into 8 pieces. I weighed each of mine - they were 97 g/3.4oz each.
Pat both of your hands in the flour and then pick up a piece of dough, flatten it slightly in your hands and then put it on the work surface and pull the edges into the centre so you have a rough ball shape. Turn the ball over and gently roll it into more of a ball shape and place onto a large baking tray with the smoothest side at the top. Cup your hands around the sides of the ball and give it a little squeeze to add a tiny bit of height. Repeat with the remaining dough - ensuring there is at least a couple of inches between each ball - as they will expand.
Place the tray in a large carrier bag - making sure none of the bag touches the dough. If the dough touches it, it will stick. Leave to prove again until almost doubled in size - about 1.5-2 hours.
Preheat the oven to 200C/400F. Whisk your remaining egg with a tsp of cold water.
Take the tray out of the bag and gently brush each of the buns all over the top and sides with egg wash. Make sure you don't have too much egg wash on your brush or it will run down the sides of the buns and pool at the bottom - leaving a crispy-eggy edge to the buns.
You can leave the buns plain, or if you prefer, sprinkle with 1 tbsp of sesame seeds or 1 tbsp everything spice.
Place the buns in the oven and cook for 15 minutes until dark golden brown. Take out of the oven and leave to cool for 5 minutes on the tray, before removing from the tray on cooling further on a cooling rack.