Slow roast pork for a crowd

I used to be very scared of my oven. It seemed to me that roasting things belonged to a higher order of cooking than the one I did. Making a curry sauce for a chicken seemed so much less daunting than locking it away in a baking hot box.
The day I found out that this is not so, but far otherwise, was a very happy one for me. An epiphany. Stout Cortez was innexpresively blasé in comparison.
Which is why one of my favourite things to serve up when I have a crowd coming is a slow roast hunk of pork. The thing has to stay in the oven for at least four hours, but half an hour up or down makes no difference. It´s better with 24 hours of previous marinating, but it´s also impressively delicious without. The marinade, or the rub, can be anything you like, and so the dish can be taken in any geographical direction. And there´s something festive in a big meaty centerpiece, a soupçon of the fatted calf old-style hospitality.
It is excellent cold, and so can be left on a table for people to carve as they will, and stuff into sandwiches, or eat with potato salad, or some quickly put together beans in vinaigrette. And rice, too, of-course. (Get a rice cooker inmediately!!!!)
As long as you don´t break the cardinal rule taught to me by my mother: have twice as much booze as you think you´ll need, and under pain of death don´t run out of ice, this makes for easy-peasy entertaining. And you won´t have to worry about smoke, or cleaning the grill.

Slow roast pork

The cut I use is aguja, which I think is pork shoulder, but just to be clear, I´ll make a nice little diagram of where in the pig it is.
It´s a cut that is pretty much self-basting, and to my mind, much more juicy and flavourful than any other. It doesn´t dry out, and it costs a fraction of the price of loin, or the little tenderloins. It´s also tear-inducingly good the next day, in sandwiches, tacos, noodles, or empanadas. So it would be very silly of you not to cook as big a piece as you can find.
My butcher usually has a joint weighing about 3 kilos, bone in. This is tastier, but more tricky to carve, so by all means have him cut it out, but don´t forget to put it in the roasting tin.
In Spain they never leave the skin on the meat, so there is no chance of crackling. But I suspect after so long, the skin would be quite tough, so I´m not sure that I´d leave it in if I could.
When not making a Chinese version, or a USA style barbecue sauce, this is my favourite. I think I took it from a NYT article about taco fillings:

Orange juice
Garlic
coriander seeds,
cumin seeds
olive oil,
peppercorns,
oregano

Quantities can vary, I think you really have to use your eyes and make it to your liking. Blitz it in a processor, put it in a freezer bag, and leave as long as you can, 24 hours max. Then strain it. You will be left with a paste in the strainer, which you will rub on the meat. The liquid, an oily and spicy orange juice, you will use to baste the piece every now and then, as and if you remember to.

Make little cuts in the meat and slide in slivers of garlic.

Then put it in the hottest oven you can for half an hour. After, turn it down very low, and leave it for four hours at least. It can stay longer, and won´t dry out, as long as we´re talking about a seriously low oven, 110ºC or so. Mine has no switches, so I don´t know exactly what goes on in there, except that it smells heavenly. Once done, you´re left with a deep brown, crusty outside, and a tender, juicy white inside.
Make sure you´re doing the carving, and can snaffle as many bits of charred outside as you can, all the while looking bountiful as you hand out every third slice.