Prepare Potatoes: Peel and grate the russet potatoes and yellow onion. Soak in cold water for 20-30 minutes, then drain and squeeze out moisture.

Mix Latke Batter: Combine potato-onion mixture, beaten egg, matzo meal, kosher salt, and black pepper in a bowl. Stir until cohesive.

Fry Latkes: Heat vegetable oil in a skillet. Drop spoonfuls of latke batter and fry for 6-10 minutes on each side until golden brown.

Poach Eggs: Simmer water with vinegar. Crack eggs into small dishes, then gently slide into water and poach for 4.5 to 5 minutes.

Make Hollandaise Sauce: Whisk egg yolks, lemon juice, and a pinch of salt in a bowl set over simmering water. Gradually whisk in melted butter until smooth.

Assemble: Place a latke on a plate, top with a poached egg and hollandaise sauce, and garnish with flaky salt and chives.