Grate potatoes and onion. Place grated potatoes in a large bowl of lightly salted water and let soak for 20 to 30 minutes or up to 1 hour.

Drain potatoes, squeezing out as much moisture as possible.

Combine grated potato, onion, egg, matzo meal, salt, and pepper in a large bowl, folding with a fork until evenly moistened.

Heat a large skillet over medium heat and add a ¼-inch deep layer of oil to the pan.

Spoon about 3-4 tablespoons of potato mixture into the hot skillet, spreading out to a 3-inch round. Cook for 6 to 10 minutes per side until golden brown, then flip and cook for another 5 to 6 minutes.

Remove from oil with a slotted spatula and place on a baking sheet to keep warm while cooking remaining latkes.

Fill a saucepan 2-inches deep with water, add vinegar, and bring to a bare simmer. Crack one egg into a small ramekin and carefully tip it into the water. Cook for 4½ to 5 minutes.

Lift egg out of the pan and place on a lightly oiled plate. Repeat with remaining eggs.

Combine egg yolks, lemon juice, and salt in a blender and blend until smooth. Melt butter and slowly drizzle into the blender with the motor running until emulsified.

If hollandaise is too thin, whisk it in a bowl over barely simmering water until thickened.

Keep the sauce warm for up to 30 minutes before serving.

Place a piece of smoked salmon and a poached egg on top of each latke. Drizzle generously with hollandaise and sprinkle with chopped chives and red onion.