Ultimate Matzo Ball Soup

Heat schmaltz in a medium skillet over medium-low. Add onion; cook, stirring often, until onion just begins to brown in spots, 8 to 10 minutes. Remove from heat, and let cool for 10 minutes.

Meanwhile, break matzo sheets into 1-inch pieces, and place in a food processor; process until mostly fine crumbs form with some small pieces of matzo sprinkled throughout, about 50 seconds, stopping to stir occasionally. Transfer ground matzo to a medium bowl, and stir in garlic powder, white pepper, and 1 1/2 teaspoons salt; set aside.

For floater matzo balls, skip to step 4. For sinker matzo balls, whisk together eggs and onion mixture in a medium bowl until no streaks of egg white remain; whisk in seltzer. Add ground matzo mixture, and stir to combine. Cover with plastic wrap, pressing directly onto surface of mixture. Refrigerate at least 2 hours or up to 12 hours. Proceed to step 5.

For floater matzo balls, separate 3 eggs, placing yolks in a medium bowl and whites in a large bowl. Add remaining 2 whole eggs and onion mixture to bowl with egg yolks, and whisk until thoroughly combined with no streaks of egg white; whisk in seltzer, and then stir in ground matzo mixture. Whisk egg whites until stiff peaks form. Fold egg whites into matzo mixture until completely combined. Cover with plastic wrap, pressing directly onto surface of mixture. Refrigerate at least 4 hours or up to 12 hours.

Bring 2 quarts chicken stock to a boil over high in a large, wide Dutch oven. Stir in 2 teaspoons salt; reduce heat to medium-high for a gentle boil. Using wet hands, roll matzo mixture into 19 balls (about 1 1/2 tablespoons each), dropping balls into stock as you roll. Return stock to a gentle simmer; partially cover, and reduce heat to very low. Simmer until matzo balls are puffed and cooked through, 35 to 40 minutes, flipping halfway through cooking time. (To test doneness, cut open one matzo ball — it should be the same color from edge to center.) Remove from heat; cover to keep warm.

Meanwhile, bring remaining 2 quarts chicken stock to a boil in a large pot over high. Stir in carrots, celery, and remaining 2 teaspoons salt. Reduce heat to medium, and simmer until vegetables are tender, about 10 minutes. Keep warm over low.

To serve, divide matzo balls evenly among bowls using a slotted spoon. Ladle stock with vegetables over matzo balls. Garnish with dill or parsley, and serve with lemon wedges.