Most recipes I see for panettone (and really most enriched doughs) specify that butter must be added bit by bit, only when the last bit is fully incorporated.
But I recently got ahold of Thomas Chambelland’s Sourdough Panettone and Viennoiserie, and every recipe in that book asks to add the butter all at once and only mix for a few minutes! I have a Kitchenaid at home but the authors do say that planetary mixers are suitable, so I don’t know if that would be the difference.
I know there are many panettone experts on this forum—does anyone have insight into this discrepancy? I’ve been having a string of panettone failures and I’m looking for any possible avenue for improvement.
I would have to go back and check my copy later when I have time to be sure, but I'm fairly sure that the butter is added in three stages for most recipes, at least for the secondo impasto.
On mixing times, my experience was that - despite the official KitchenAid recommendations - "low" speed is 2 and "high" speed is 4. Depending on the size and hydration of the dough at any given stage in the process, it may also be helpful to use the paddle rather than the hook. The same general principles apply as for making high hydration ciabatta or pan de cristal.