Blend half of the white onion, half a bar of achiote paste (usually the package has two bars stuck together, just use one), breaking up the achiote as you add it. Add 4 garlic cloves, 4 peppercorns, half the orange juice, half the lime juice, and salt to taste. The mixture should be thick and citrusy—taste and adjust salt as needed.

Cut the pork into medium pieces. Sear the meat in a pot with a lid or a pressure cooker.

Cook the pork, adding the achiote sauce you just made. If using a pressure cooker, cook for about 30 minutes; in a regular pot with a lid, cook for about 45 minutes, making sure the pot is tightly covered. Watch the meat as it cooks to prevent sticking, drying out, or burning.

In the same blender (without washing after the achiote sauce), add the remaining white onion, the rest of the orange juice and lime juice, the remaining peppercorns and garlic cloves. You can also add one habanero pepper if you like—it’s optional. Blend and set aside; you’ll use this as extra juice for the meat.

Once the pork is cooked, shred it using two forks. Add the reserved juice from the blender and finish cooking.

To serve with the tacos, thinly slice the red onion and finely slice two habanero peppers, removing the seeds and centers to reduce the heat. Add lime juice, salt, and pepper. Mix well.