How to Make It
In a colander set over a large bowl, toss the potatoes with the onion and squeeze dry. Let the potatoes and onion drain for 2 to 3 minutes, then pour off the liquid in the bowl, leaving the starchy paste at the bottom. Add the potatoes and onion, along with the eggs, scallions, matzo meal, butter, salt, pepper and baking powder; mix well.
In a large skillet, heat an 1/8-inch layer of oil until shimmering. Spoon 1/4-cup mounds of the latke batter into the skillet about 2 inches apart and flatten slightly with a spatula. Fry the latkes over moderately high heat, turning once, until golden and crisp, 5 to 7 minutes. Transfer the latkes to paper towels to drain, then transfer to a platter. Repeat to make the remaining latkes, adding more oil to the skillet as needed. Serve with applesauce, sour cream, smoked salmon and salmon roe.