Goldrush, a recent apple cultivar, has a nice balance of sweetness and acidity that's ideal for this salad. Other suitable varieties include Albemarle (Newtown) Pippin, Honeycrisp, Pink Lady, Golden Russet, and Roxbury Russet.
Combine first 6 ingredients, stirring well with a whisk.
Combine onion, spinach, and apple in a large bowl. Drizzle with dressing; toss gently to coat. Sprinkle with cheese.
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