Although the ingredient list looks long, you can actually make everything well in advance, and separately. The flour for the arepas is precooked corn meal and is sold as masarepa or masa precocida. This recipe makes about 60 hors d'oeuvres.
1 medium red onion, cut into 3/4-inch-wide wedges, then very thinly sliced crosswise
1 to 2 habanero chiles, seeded, deveined, and very finely chopped
1/2 cup distilled white vinegar
1/2 tsp. dried oregano (preferably Mexican), crumbled
1/2 tsp. salt
1/2 tsp. cumin seeds
1/2 tsp. black peppercorns
1/4 tsp. allspice berries
2 tbsp. achiote (annatto) seeds
6 large garlic cloves
1 1/2 tsp. salt
1 tsp. dried oregano (preferably Mexican), crumbled
1/3 cup fresh orange juice
1/3 cup distilled white vinegar
3 lb. pork shoulder chops (3/4 inch thick)
3 cups whole milk
4 tablespoons (1/2 stick) unsalted butter, cut into pieces
1 1/2 cups white arepa masa
1 tbsp. sugar
1 tsp. salt
1 cup coarsely grated mozzarella cheese
2 1/2 tbsp. vegetable oil
1. Make the pickled onion: In a bowl, combine onion, chiles, vinegar, oregano, and salt. Cover and chill for at least 12 hours.
2. Meanwhile, marinate the pork: In a dry heavy skillet, toast cumin, allspice, and peppercorns together over medium heat, stirring, until fragrant, 1 to 2 minutes. Finely grind toasted spices with achiote in an coffee/spice grinder or with a mortar and pestle.
3. Mince garlic and mash to a paste with the salt using a heavy knife, then transfer to a 2 1/2- to 3-quart shallow glass or ceramic baking dish. Stir in spice mixture, oregano, orange juice, and vinegar. Add pork and rub meat all over with marinade. Marinate pork, covered and refrigerated, for at least 2 hours.
4. Preheat the oven to 325°F. Let the pork return to room temperature. Add 1/2 cup water to baking dish and cover tightly with foil. Bake in middle of oven until very tender, 1 3/4 to 2 hours. (Leave oven on to reheat the arepas.)
5. Meanwhile, make the arepas: Bring milk to a simmer in a small saucepan, then remove from heat and set aside 1/2 cup in a small bowl. Add butter to hot milk remaining in saucepan and stir until melted.
6. In a large bowl, toss together arepa masa, sugar, salt, and mozzarella. Add hot milk with butter and stir until combined. Let mixture stand until milk is absorbed, 1 to 2 minutes (dough will be soft; it will continue to stiffen as it stands).
7. Form 1 level tablespoon dough into a ball. Flatten ball to a 1 1/2- to 1 3/4-inch-diameter disk and transfer to a wax-paper-lined tray. Repeat with remaining dough, stirring in some of reserved milk if dough becomes too stiff and edges of disks crack when flattened.
8. In a 12-inch nonstick skillet, heat 1/2 tablespoon oil over medium-low heat until hot. Working in batches of 10 to 12, add the arepas and cook, turning over once, until golden in patches, 8 to 12 minutes. (Add more oil to skillet between batches as needed.) Transfer them to baking sheets as they are cooked.
9. When the pork is done and cool enough to handle, shred meat on a cutting board, discarding bones and excess fat. Return meat and any juices accumulated on cutting board to the baking dish.
10. If the arepas were done in advance, cover them with foil and place in the oven until heated through, 10 to 15 minutes. Serve warm, topped with pork and pickled