Preheat the oven to 180°.
In a large bowl, whisk together all the dry ingredients except the sugar.
Heat the milk in a saucepan until lukewarm.
In a separate bowl mix the yeast and sugar until completely dissolved and liquid.
Now add the eggs, yeast and milk to the dry ingredients and mix until well combined.
Add the butter a few cubes at the time, then add the orange zest until you get an even dough.
For more elasticity, kneed a few more time with your hands, then cover the dough in cling film and to sit for at least 50 minutes.