Everything Bagel Stuffing

Preheat oven to 350 degrees F. Lightly oil a 3-quart baking dish and set aside. In a large skillet over medium-high heat, heat 2 tablespoons oil. Add onions and celery and season with 1/2 teaspoon salt and 1/4 teaspoon pepper. Cook, stirring often, until vegetables are tender, 6 to 8 minutes. Add vinegar and cook, scraping up any brown bits, until evaporated, about 1 minute. Transfer vegetables to a large bowl. Add bagel pieces, chives, and sage and toss to combine. In a separate medium bowl, whisk together eggs, sour cream, and 2 cups broth. Pour over bread mixture and toss until evenly moistened, adding more broth 1/4 cup at a time until bagel pieces seem hydrated (you might not use it all). Transfer mixture to prepared baking dish and dot top with butter. Cover dish with foil and bake until a knife inserted in the center of the stuffing comes out warm, 30 to 35 minutes. Increase heat to 425 degrees and continue baking until top is deeply golden, 10 to 15 minutes more. Let rest 10 minutes before serving. Meanwhile, in a small skillet over medium heat, heat vegetable oil. Add garlic and cook until golden brown, 2 to 3 minutes. Transfer to paper towels using a slotted spoon. Add shallot to oil and cook until golden, 4 to 6 minutes. Transfer to paper towels using a slotted spoon. Let garlic and shallot cool slightly, then add to a small bowl with poppy seeds and sesame seeds. Serve stuffing sprinkled with poppy seed mixture and garnish with chives.