Chicken, leeks, and carrots swim in a fragrant broth, but the star is the comforting matzo ball. Seltzer and baking powder are the keys to making airy spheres; their richness comes from the chicken fat, or, as Jewish bubbes call it, schmaltz.
Whisk together matzo meal, 1 tablespoon salt, pepper, and baking powder. In a large bowl, lightly beat eggs; whisk in chicken fat, matzo mixture, and seltzer until thoroughly blended. Cover and refrigerate at least 2 hours and up to 1 day.
Bring a large pot of salted water to a boil. With lightly dampened hands, form heaping 1/3 cupfuls of batter into 8 balls. Gently drop balls, one at a time, into boiling water. When they all float, cover pot. Reduce heat to a gentle boil; cook 20 minutes. With a slotted spoon, gently transfer matzo balls to a tray lined with a clean kitchen towel. Let cool 15 minutes, then cover tray tightly with plastic wrap. If not using immediately, refrigerate up to 1 day.
In a pot, combine stock, chicken, carrots, lemon peel, and 4 teaspoons salt. Bring to a boil, then reduce to a simmer; cook, partially covered, until chicken is just cooked through, about 35 minutes. Transfer chicken to a plate; let cool 10 minutes. Add leeks and simmer until just tender, 6 to 8 minutes. Pull chicken from bones; discard bones. Return chicken to pot and add matzo balls; bring to a simmer and heat through. Stir in dill; serve.