Bought a pork loin at Costco. Wonderful value but not enough fat on
it; it would dry out too quickly. Decided to put the fat inside it so
it would contribute moisture and flavor.

Froze some Italian sausage links for a few hours to firm them.

Cut a piece about a foot long from the loin and pushed a thin-bladed
French chef's knife through it lengthwise down the center. Essentially
made a tube of the piece of loin with a slot all the way through it.
Pushed the sausage links all through the loin. Roasted it at 275F
until the sausage was 145F on my quick-read thermometer.  Let it rest
for 15 minutes and sliced it. Beautiful.

The pork had a circular slice of sausage in the middle of every slice
of the pork and the seasonings had permeated the meat from the inside.
Most of the fat cooked out of the sausage, but enough was there to
give the roast a wonderful sense of moistness.

Easy to do, pretty to serve, tasty to eat.

Pastorio