Peel potatoes and cut into 1-inch pieces. Cover with cold water in a medium pot, stir in 1 teaspoons salt and simmer until very tender, about 18 minutes.
Drain potatoes, then mash in a bowl.
Cook scallions with 1/4 teaspoons each salt and pepper in 2 tablespoons annatto oil over med. heat, stirring, until scallions are softened, then stir into potatoes along with cheese. Form mixture into 8 balls and flatten each into a 3-inch patty.
Heat 1 tablespoons annatto oil in a 12-inch nonstick skillet over med.-high until hot, then fry cakes in 2 batches, turning over once, until crusty, about 6 minute per batch. add remaining oil for second batch.