Remove the lime and orange zest with a vegetable peeler. Pork butt roast is often labeled Boston butt. Do not overtrim the pork; this extra fat is essential to keeping the pork moist and helping it brown when sautéed in step 3. We like to serve carnitas with warmed corn tortillas and a variety of toppings, like finely chopped onion, fresh cilantro leaves, thinly sliced radishes, sour cream, and lime wedges.

Combine pork, onion, orange zest and juice, lime zest and juice, garlic, cumin, oregano, 2½ teaspoons salt, 1½ teaspoons pepper, and bay leaves in slow cooker. Cover and cook until fork slips easily in and out of pork, 5 to 7 hours on high or 8 to 10 hours on low.

Using slotted spoon, transfer pork from slow cooker to large bowl. Using potato masher, smash pork until coarsely shredded. Strain cooking liquid from slow cooker through fine-mesh strainer set over separate bowl and discard solids.

Heat oil in 12-inch nonstick skillet over medium-high heat until shimmering. Add pork to skillet. Whisk cooking liquid to recombine, then add 1 cup to skillet with pork. Cook, stirring occasionally, until liquid has evaporated and pork is evenly browned and crispy in spots, 10 to 15 minutes.

Season with salt and pepper to taste. Transfer pork to serving platter and moisten with ¼ cup remaining cooking liquid, or more as needed. Serve.