Heat 2 tablespoons of vegetable oil in a large pot over medium heat. Add the diced onion, sliced carrots, and sliced celery. Sauté until the vegetables soften and the onion becomes translucent, about 5–7 minutes.
Pour in the chicken stock, then stir in the kosher salt and black pepper. Bring the broth to a rolling simmer, then reduce heat to maintain a gentle bubble for 10 minutes to meld the flavors.
For the Matzo Balls
While the soup simmers, whisk together the eggs, vegetable oil, kosher salt, and baking powder until glossy. Gently fold in the matzo meal and water until just combined, then cover and chill the mixture for 20 minutes.
Return the broth to a gentle simmer. Use two spoons to drop heaping tablespoonfuls of the chilled matzo batter into the pot. Cover immediately and simmer undisturbed for 25–30 minutes, until the matzo balls are tender with a slight bite.
Notes
Prep Testing Note: Resting the matzo meal mixture for 20 minutes chilled yields dough that’s firm enough to shape easily and produces a silkier texture.Cooking Testing Note: Avoid lifting the lid during the 25–30 minute steam, or the matzo balls will deflate; patience ensures light, lofty dumplings.Storage Testing Note: Store matzo balls separately from broth to maintain their pillowy texture; when kept apart they stay tender, not waterlogged.