- 2 medium red beets (about 8 ounces total)
- 1/4 cup fresh lemon juice
- 2 tablespoons prepared horseradish
- 1 tablespoon Sherry vinegar
- 1/2 cup extra-virgin olive oil
- Kosher salt
- 1 12-ounce skinless cod or pike fillet
- 5 tablespoons (or more) vegetable oil, divided
- 8 ounces smoked whitefish, skin and bones removed, flaked
- 3 large eggs, beaten to blend
- 1 large shallot, finely chopped
- 1 piece matzo, finely crushed (about 1/4 cup)
- 1/4 cup chopped fresh chives
- 2 tablespoons chopped fresh dill plus more for serving
- Freshly ground black pepper
- Preheat oven to 400°F. Wrap beets individually in foil, place on a rimmed baking sheet, and roast until tender, 50-60 minutes. Let cool. Peel and cut into 1/4″ cubes.
- Whisk lemon juice, horseradish, and vinegar in a medium bowl; gradually add oil, whisking to blend well. Season with salt. DO AHEAD: Beets and vinaigrette can be made 1 day ahead. Cover separately and chill.
- Heat oven to 400°F. Place cod on a rimmed baking sheet. Rub with 1 tablespoon oil. Roast until just opaque in center, 10-15 minutes. Let fish cool, then flake with a fork.
- Mix cod, whitefish, eggs, shallot, matzo, chives, 2 tablespoons dill, and 2 tablespoons water in a medium bowl. Season with pepper and mix vigorously to combine (mixture will be stiff). DO AHEAD: Fritter mixture can be made 1 day ahead; cover and chill.
- Reduce oven temperature to 200°F; set a wire rack inside a large rimmed baking sheet. Heat remaining 4 tablespoons oil in a large skillet over medium-high heat. Working in batches, drop scant 1/4-cupfuls of fritter mixture into skillet; press gently with a spatula to flatten. Cook, turning once and adding more oil if needed, until golden brown and crispy around edges, about 4 minutes per batch. Transfer to prepared rack. Keep warm in oven while cooking remaining fritters.
- Mix beets into vinaigrette. Serve fritters with vinaigrette; top with dill.