Add the potatoes to a large pot and cover them with at least 4 inches of cold water. Bring the water up to a gentle boil over medium-high heat and boil the potatoes for 20 minutes, or until a knife can pass through the center of the largest potato without resistance.
Once soft, drain the potatoes in a colander and leave them to cool completely.The rest of the ingredients will be added once the potatoes are cool.
Cook, then Cool the Picadillo
Heat a large pan over medium heat. Add the meat to the pan and cook the meat just until it starts to brown, about 2-3 minutes.
Add the green pepper, onion, and garlic to the pan. Sauté the meat until it is brown and the veggies are translucent, stirring occasionally, about 3 or 4 more minutes. Once browned, drain any excess fat from the meat and return it to the stove.
Stir the sofrito, adobo, sazón, garlic and onion powders, oregano, and pepper into the meat. Heat these until fragrant or 1-2 minutes. Add the tomato sauce, sliced green olives, and capers to the pan.
Heat the sauce over medium heat, stirring frequently, for 2-3 minutes, or until the picadillo begins to dry out slightly. The picadillo is done when it is thick, but not dry- like wet taco filling.
Transfer the picadillo to a sheetpan and smooth it into an even layer. Cover the pan with plastic wrap and allow it to cool completely in the refrigerator.
Finish the Mashed Potato Mixture, Then Cool
Once the potatoes are completely cooled, grate them into a large mixing bowl. Stir in the beaten egg, then use a potato masher (or fork) to mash them into a paste.
Add the cornstarch and bijol to mixture and use your hands or a spoon to combine the mixture completely. The mixture should be pliable without being runny or too stiff. Press the potato mix against the sides of the bowl to help it cool down faster. Place a piece of plastic film against the potatoes to keep them from drying out, then put the bowl in the fridge to chill them completely- at least 1 hour.
Fill the Potatoes, Then Coat
Set up the bowls of potato and picadillo near one another. Sift together the 1/4 cup of cornstarch and bjiol onto a small sheetpan.
Divide the potato mixture in the bowl into 12 equal portions using a rubber spatula, about 1/2 cup each. Lay the plastic wrap you covered the potatoes in the bowl with over your hand and place a portion of the potato mixture into the center of your palm.
Use the opposite hand to press the potatoes into a 1/4" thick disc. Place a mound (about 3 tablespoons worth) of chilled picadillo into the middle of the potato disc. Close the fingers of the plastic-covered hand to bring the potato mix up, and around, the picadillo, then gently pinch the potato mixture together to close the seam. Try make sure you're encasing the picadillo in the potatoes, with the least amount of filling poking out. Don't get frustrated.Add a little potato to any cracks in the surface if need be. Use the plastic wrap to smooth any cracks or crevices.
Carefully lay your formed rellenos on a sheet pan while you mold the rest. Begin heating your frying oil over moderate heat to 360°F.
*If you plan to air fry or bake the rellenos, skip the dusting of cornstarch. Once all of the rellenos are formed, dust your hands liberally with some of the cornstarch from the dusted sheet pan. Grab a papa and toss it gently back and forth to give them a light dusting of cornstarch. Too heavy a dusting will leave untasty clumps of cornstarch on the rellenos after frying.
Fry the Rellenos de Papa
See notes in post on how to deep-fry safely. Once the oil reaches temperature, use a slotted spoon, preferably wooden, to gently slide a 2-3 rellenos into the hot oil. It's okay if the relleno sticks slightly to the sheet pan when you attempt to lift it. Just scrape up what was left behind and mold it back onto the relleno.
Fry your rellenos for 6 minutes. After 1 minute of frying, use a flat spider to nudge the papas from the bottom of the pot. This helps them brown evenly without one side burning. Swish them around in the oil, carefully, as they cook to keep them from frying too close to one another.
If the rellenos fall apart as soon as they hit the oil it is because they either aren't cold enough, or because you added too many eggs to the potato mixture (which shouldn't be the case). If it's the former, pop the sheet tray of rellenos into the fridge for an hour and try again. If it's the latter,try the fridge trick and if that doesn't work, brush them with oil and bake them, instead.
Once the rellenos are done frying, use the spider to lift them from the oil and transfer them to a rack placed over a sheet pan and allow them to drain thoroughly. Continue frying the rellenos, making sure to allow the oil to come back up to temp before adding the next batch.
Arrange the rellenos on a platter or wrap each relleno in deli paper. Serve with a bowl of mayo-ketchup (recipe below). Enjoy while hot.
If you choose to make your picadillo with ground chicken, meat alternative, or turkey, you need to add a tablespoon of oil to your pan before browning it.
Preheat the air fryer to 400°F on the air fry setting.
Lightly grease the tray before arranging the potatoes on it, making sure to leave space around each to allow the air to circulate around them.
Brush a very light coating of oil on the outside of the potato.
Air fry the potatoes for 15 minutes. If they become too brown, carefully flip them over to the other side before continuing to cook.
Cook in batches to avoid soggy rellenos.
Preheat your oven to 450°F.
Arrange the rellenos, with space around each, on a parchment-lined sheet pan.
Bake them for 20 minutes or until slightly browned.
Mayo-Ketchup Dipping Sauce:
1 cup mayonnaise 1/4 cup ketchup 1/2 teaspoon granulated garlic 1/2 teaspoon adobo seasoning
In a small bowl combine the mayo, ketchup, garlic powder, and adobo.
Stir the mixture together until combine.
Serve immediately or store, covered, in the refrigerator for up to a week.
Arrange the rellenos on a lightly greased sheet pan. Reheat in a 400°F for 5-10 minutes, or until warmed through.
Don't dust the rellenos in the cornstarch prior to freezing.
Lay the formed potatoes on a lightly greased sheet pan and freeze until solid. Transfer the frozen papas to a freezer storage bag and store for 6 months or less.
When you're ready to cook, thaw the rellenos slightly in the fridge (for about an hour). Dust with cornstarch, then fry for 7 minutes, instead of six. The extra minute accounts for them being partially frozen.
I don't recommend freezing fried rellenos because the exterior becomes really soft and soggy after thawing and reheating. If you do, however, freeze and store the fried ones the same way (on a lined sheet pan). Thaw them for 30 minutes to an hour and reheat until warmed through in a 350°F oven or in the air fryer.