1 pound (1 pint) plain yogurt
1 hothouse cucumber, peeled and seeded
1 tablespoon plus 1/2 teaspoon kosher salt
1/2 cup sour cream
1 tablespoon Champagne vinegar or white wine vinegar (I prefer Champagne, I think it tastes crisper)
2 tablespoons freshly squeezed lemon juice (1 lemon)
1 tablespoon good olive oil (see Liz's post below!)
1 1/2 teaspoons minced garlic
1 1/2 teaspoons minced fresh dill
Pinch freshly ground black pepper
Place the yogurt in a cheesecloth or paper towel-lined sieve and set it over a bowl. Roughly grate the cucumber and toss it with 1 tablespoon of kosher salt; place it in another sieve, and set it over another bowl. Place both bowls in the refrigerator for 3 to 4 hours so the yogurt and cucumber can drain.
Transfer the thickened yogurt to a large bowl. Squeeze as much liquid from the cucumber as you can and add the cucumber to the yogurt. Mix in the sour cream, vinegar, lemon juice, olive oil, garlic, dill, 1/2 teaspoon salt, and pepper. You can serve it immediately, but I prefer to allow the tzatziki to sit in the refrigerator for a few hours for the flavors to blend. Serve chilled or at room temperature.