1. Cook the linguine according to the package directions. Reserve 2 tablespoons of the pasta water before draining.
2. While the pasta cooks, make the clam sauce: In a skillet over medium heat, warm the butter until hot, about 2 minutes. Sauté onion and garlic 1 minute. Add salt and pepper; continue to sauté another minute, or until onion is soft and garlic is fragrant but not browned. Add the drained chopped clams and reserved 2 tablespoons clam juice; stir gently to combine, and simmer.
3. Add reserved 2 tablespoons pasta water to the skillet with the sauce. Stir sauce, and continue to simmer 3 minutes or until slightly thickened.
4. Toss the linguine with olive oil and divide between two bowls. Top each serving of pasta with half of the clam sauce, 1 tablespoon cheese, and a sprinkling of chopped scallion.