Grate 2 large russet potatoes and 1 yellow onion using a food processor for a fine texture. Soak in lightly salted water for 20-30 minutes.

Drain the mixture thoroughly and squeeze out any moisture. Combine with 1 beaten egg, matzo meal, salt, and pepper. Mix until well combined.

Heat vegetable oil in a skillet over medium-high heat until shimmering. Form latke mixture into rounds and fry for 6-10 minutes per side until golden brown.

Poach eggs in simmering water with vinegar for 4½ to 5 minutes, then drain on a paper towel.

Blend 3 egg yolks with 1 tablespoon lemon juice and a pinch of salt. Slowly drizzle in 1/2 cup melted butter to create hollandaise.

Assemble the dish by placing a warm latke on a plate, topping it with salmon, poached egg, and hollandaise. Garnish with chives and flaky salt.