Heat skillet to medium-high, and add a spoonful of bacon fat or oil. Sear roast on all sides.
Heat slow cooker to high heat. Add broth, seasonings, garlic, and sliced onion. Mix well.
When roast is browned well, add to slow cooker. Cook on LOW HEAT for 8-9 hours.
To test for doneness, stick a fork into teh meat and twist, If the meat twists out easily, it is done. If not, let it cook for 30-60 more minutes before checking again.
When meat is done, place roast on cutting board and slice into thick pieces. Place back into juices and stir or use forks to shred. Serve with warm tortillas and a squeeze of lime, if desired.
Notes
The meat freezes well once cooked. Cool and place into freezer bags and label. You can use tongs to remove meat from juices.