My boss wants me to half cook bacon, then finish cooking it the next day to serve our customers at breakfast. Is this safe?
The questions already asked are key: Will it be refrigerated and would you consider half cooked to be less safe than raw for a day?
To be safe, it would need to be promptly cooled to 40F or less and kept there. But, I would have another question for you to consider, is it fresh bacon, cured, cured and smoked or oven finished?
If cured and smoked, or oven finished, then it has already been treated in a preserving way and then cooked to typically 150 degrees, so this largely answers your question on if it is considered safe. It has already been done. If it is cured but not smoked, it likely has still been cooked, or half cooked if you will to the same temperature, just without smoke, but even if not logic would follow that it would be considered safe as long as you followed refrigeration standards and promptly. Fresh bacon though I would put in a complete different ballpark and I would be very hesitant to consider doing that, or even cured if it was slab rather than typical slices.
Now, the next question though is "Is it worth it?" What does it really gain you? If you properly cool half done bacon, now you have to reheat it from cold to serving temperature while finishing rendering the fat and cooking it the rest of the way without over cooking it. In my personal opinion, the end result is likely to be inferior quality though I like bacon less crispy and dried out than many people prefer. I would much prefer it cooked freshly, but as I make my own bacon I am pretty picky on what I consider good bacon. Note though that it really is not that uncommon, especially in fast food places and some breakfast diners, for bacon to be cooked ahead of time and then just reheated often in a microwave. I don't like it, but many are fine with it.
All that of course is assuming you are talking about typical US belly bacon. I would be very much against doing any of that with say a good back bacon, but it might still be safe. Just very low quality.
If you have access to a sous vide cooker, do your bacon in it at 145°F for 8 hours (up to 2 days), then refrigerate it if you're not going to cook it right away. Thick-sliced is best. The bacon cooks very quickly (some people only brown one side briefly) and is great! http://www.seriouseats.com/2016/11/how-to-make-juicy-sous-vide-bacon.html