Cook rice in 1 1/2 cups water until completely tender throughout the kernel, about 1 hour or more. Drain rice in colander and let sit until it is dry to the touch, about 15 minutes. Place warm rice in a mixing bowl.
Using paper towels, squeeze as much moisture as possible from potato, a handful at a time and transfer to the bowl with the rice. With a fork, mix in the egg and scallions. Sprinkle with flour and mix in. Add salt and pepper to taste.
Coat a large skillet with cooking spray until well coated. Place over medium-high heat.
Place rounded tablespoons of the mixture in the pan, one at a time, pressing each firmly with the back of a fork to make thin, 2-inch pancakes with lacy edges. Space latkes 2 inches apart. When lightly browned on the bottom, 2 to 3 minutes, gently turn latkes and brown on the other side, about 2 minutes. (To avoid splattering oil, use a splatter screen.) When done, transfer to a warm plate and keep warm. Repeat with remaining mixture, re-spraying pan before adding more pancakes. Serve immediately.