Make the matzah ball dough: In a bowl, whisk eggs with oil or schmaltz until well combined. Add matzah meal, salt, pepper, and seltzer water. Mix gently until just combined. Cover and refrigerate for 20 minutes.

Prepare the broth: In a large pot, bring chicken broth to a simmer. Add carrot, celery, and onion. Let simmer while you form the matzah balls.

Form the matzah balls: Wet your hands with cold water. Take about 1 tablespoon of the chilled dough and gently roll into 1-inch balls. Don't overwork the dough - this keeps them light.

Cook the matzah balls: Gently drop the formed balls into the simmering broth. Cover the pot and let cook for 20 minutes without lifting the lid - this creates steam for fluffy balls.

Check doneness: After 20 minutes, carefully remove one matzah ball and cut it in half. It should be light and fluffy all the way through with no dense spots.

Serve: Ladle the hot broth with vegetables into bowls. Add 2-3 matzah balls to each serving. Garnish with fresh dill and serve immediately.