Serve this salad as a simple side that comes together in just 20 minutes.
Preheat oven to 350 degrees. Bring a large pot of salted water to a boil. Spread pine nuts on a rimmed baking sheet and toast until golden, 8 to 10 minutes; let cool.
Meanwhile, prepare a large bowl of ice water; place a colander inside bowl. Line a baking sheet with a double layer of paper towels. Cook brussels sprouts in boiling water until bright green and tender, about 1 minute. With a wire skimmer or slotted spoon, transfer to colander to stop cooking. Cool completely in ice bath, then transfer to lined baking sheet to drain; pat dry.
In a medium bowl, whisk together vinegar and oil. Add apple, brussels sprouts, and toasted pine nuts; season with salt and pepper, and toss to combine.