1. Mince and mash garlic to a paste with kosher salt using a large heavy knife, then add anchovy and capers and finely chop. Transfer mixture to a large bowl and whisk in lemon juice and pepper, then add oil in a slow stream, whisking until combined well.
2. Cook cauliflower in a 4-quart saucepan of boiling salted water until crisp-tender, 4 to 5 minutes. Drain well in a colander, then toss hot cauliflower with dressing. Cool to warm, tossing occasionally, then add parsley and toss to coat. Serve immediately.
3. Cooks' note: Dressing can be made 2 hours ahead and kept at room temperature.