2 tbsp. extra-virgin olive oil
1 1⁄2 tsp. achiote seeds (optional)
4 sour oranges
30–35 medium shrimp (about 1 lb.),
peeled and deveined, shells reserved
1 tbsp. whole allspice
6 sprigs cilantro, plus 2 tbsp. finely chopped
Kosher salt, to taste
1⁄4 cup fresh lime juice
14 small ají dulce or orange or red habanero peppers,
stemmed, seeded, and thinly sliced
3 cloves garlic, finely chopped
1⁄2 small red onion, thinly sliced
1 red habanero pepper, stemmed, seeded, and halved
1. Heat the oil and achiote seeds in an 8" skillet over medium heat and cook, stirring occasionally, until the oil is red and fragrant, 4–5 minutes. Strain the oil through a sieve and set aside; discard the achiote seeds. (If you're not using achiote seeds, simply omit the preceding step and use the olive oil on its own as instructed below.) Zest half of 1 orange; set zest aside. Juice the oranges to make 3⁄4 cup juice; set juice aside.
2. Bring the shrimp shells, allspice, cilantro sprigs, reserved orange zest, salt, and 4 cups water to a boil in a 4-qt. saucepan. Reduce heat to medium-low and simmer the broth mixture for 10 minutes. Strain the shrimp broth through a fine sieve set over a medium bowl; discard solids. Add the shrimp to the bowl containing the strained broth and poach until shrimp are just pink and cooked through, about 5 minutes. Using a slotted spoon, transfer the shrimp to a plate. Set aside 1⁄4 cup of the broth; freeze the remaining broth for another use.
3. Slice the shrimp in half lengthwise and transfer to a medium bowl. Add the reserved achiote oil and broth, orange juice, chopped cilantro, lime juice, ají dulce peppers, garlic, red onions, and habanero pepper; stir to combine and cover with plastic wrap. Refrigerate to let the flavors meld for 1 hour before serving.