Boil potatoes in salted water until very tender, 15–18 minutes. Drain well.
Mash potatoes with butter, 1 teaspoon salt, and black pepper until smooth. Mix in cornstarch. Cool to room temperature.
Warm 1 tablespoon oil in a skillet. Soften onion and bell pepper over medium heat, 4–5 minutes.
Stir in garlic. Cook 30 seconds. Add ground beef and brown, breaking it up, 5–6 minutes.
Blend in tomato paste, cumin, oregano, smoked paprika, and remaining 1/2 teaspoon salt. Cook 1 minute.
Fold in olives and raisins. Remove from heat and cool. Stir in cilantro.
Divide cooled potato mixture into 8 portions. Flatten one portion in your palm and spoon on some beef filling.
Seal the filling inside, shaping into a ball or oval. Repeat with remaining portions.
Set up breading: place flour in one bowl, whisk water into a loose slurry in another, and add breadcrumbs to a third.
Dredge each croquette in flour, dip in slurry, then coat evenly in breadcrumbs. Chill 10 minutes.
Heat oil to 350°F in a deep pot. Fry in batches until golden brown, 3–4 minutes, turning as needed.
Drain on a rack or paper towels. Rest 3 minutes before serving.