Cook up the bacon. Save the fat; you'll need 2-3 ounces (1/4-3/8 of a cup). Let the fat cool a bit and then add it to the second bourbon bottle. Add as much of the first bottle as will comfortably fit into the second bottle. Make yourself a cocktail or something with the remaining bourbon before tomorrow, and save the bottle. Cap the bourbon/fat mixture and leave at room temperature for 4 hours. Place the bottle in the freezer on its side, freeze overnight. The bacon fat will harden into a slab on top of the bourbon, and the spout will remain useable. The next day, transfer the contents of frozen bottle to the empty bottle. You can strain it if you'd like, but I don't bother.
You can drink it neat, at room temperature (but you should store it in the fridge when you're not drinking it, just in case). It's also quite nice mixed with root beer.
My impetus to first making this was a vodka and grilled cheese party a couple of years ago. The idea was that everyone bring an infused vodka and there would be bread and cheese provided as well as many pans so we could eat grilled cheese sandwiches. I heartily endorse such ideas.
I made a jalapeño, lime, and mint infused vodka (wash and cut jalapeño lengthwise, put it in for a week; bruise the mint, put it in for last 24 hours; squeeze the juice of a lime into bottle and give a good shake before serving) but wanted to try bacon. My friend Nate was already going to make bacon vodka (sub vodka for the bourbon, otherwise it's the same; makes a great Bloody Mary) so I decided to try infusing bourbon instead. I'd read about it, but was still a little wary. So glad I pushed through.
Other meat fats could be used, I'm sure. I've seen a venison whisky recipe. I do have a tub of duck fat at home...