Using a food processor fitted with a coarse grating disk, grate the potato and onion; discard any large pieces. Transfer the mixture to a clean dish towel and squeeze out any excess liquid, then transfer to a large bowl. Stir in the flour, egg, 3/4 tsp. salt, 1/4 tsp. pepper and the baking powder.
Soak 1/2 cup raisins in 1/4 cup boiling water for 10 minutes; drain and chop. Zest half a lemon. Remove remaining peel and pith from lemon half, then finely chop 1 tbsp. of the fruit. Combine raisins, zest, lemon, 2 tbsp. chopped cilantro, 1/4 tsp. ground cumin, pinch cayenne and pinch salt. To food processor, add 2 large carrots (about 6 oz.) with potato and onion.
In a medium skillet, heat 1/4 inch oil over medium-high heat until hot but not smoking. Working in 5 to 6 batches, drop 2-tbsp. scoops of batter into the pan about 2 inches apart. Using a spatula, flatten the batter into disks. Cook, turning once, until browned and crisp, about 5 minutes. (Lower the heat if the latkes darken too quickly.) Drain on paper towels. Serve with raisin topping.