Bring a large pot of water to a rolling boil over high heat. Add the 12 ounces (340 g) of rotini pasta and cook according to the package directions, usually 8 to 10 minutes, until al dente. The pasta should be tender but retain a slight firmness in the center. Avoid overcooking because very soft pasta can become mushy after mixing with the dressing.

Transfer the cooked pasta to a large colander and rinse under cold running water until no longer warm. Shake the colander thoroughly to remove excess water. Allow the pasta to drain and finish cooling for approximately 10 minutes, stirring occasionally to release trapped moisture. The pasta should feel cool and should not have visible water collecting between the spirals. Excess moisture can dilute the dressing.

Wash and dry the 2 English cucumbers: Cut them lengthwise into quarters, then slice crosswise into approximately 1/2-inch (1.3 cm) pieces. If the cucumbers contain unusually large, watery seed cavities, scoop out some of the seeds before chopping. Pat the cucumber pieces dry with a clean kitchen towel or paper towels. This helps maintain a creamy dressing rather than a watery one.

Finely dice the 1/2 cup (80 g) red onion. Chop the 1/4 cup (10 g) fresh dill and 2 tablespoons (8 g) fresh parsley. Keep the onion pieces relatively small so they distribute evenly throughout the salad without overpowering individual bites. For a milder onion flavor, rinse the diced onion briefly under cold water and dry it thoroughly before adding it to the salad.

In a medium mixing bowl, combine: 1/2 cup (120 g) sour cream 1/2 cup (115 g) mayonnaise 2 tablespoons (30 ml) lemon juice 1 tablespoon (15 ml) white wine vinegar 1 teaspoon (5 g) Dijon mustard 1 teaspoon (4 g) granulated sugar 1/2 teaspoon (3 g) fine salt 1/4 teaspoon (0.5 g) black pepper 1/4 teaspoon (0.8 g) garlic powder Whisk until the mixture becomes smooth, creamy, and evenly blended. The dressing should be thick enough to coat a spoon but loose enough to fold easily through the pasta.

Transfer the cooled, well-drained pasta to a large mixing bowl. Add the diced cucumbers, red onion, chopped fresh dill, and parsley. Gently toss until the vegetables and herbs are distributed throughout the pasta. The mixture should look colorful and evenly combined, with plenty of cucumber pieces visible.

Pour the creamy dill dressing over the pasta mixture. Using a large spoon or silicone spatula, gently fold everything together until the pasta and vegetables are evenly coated. Scrape the bottom and sides of the bowl to incorporate any dressing that settles underneath. Avoid vigorous stirring, which can damage the pasta or crush the cucumber pieces.

Taste a small spoonful of the salad: If needed, add a little additional salt to bring out the cucumber and herb flavors. The dressing should taste lightly tangy, creamy, and fresh, with a noticeable but balanced dill flavor. Remember that the pasta will absorb some of the dressing as the salad chills.

Cover the mixing bowl tightly with plastic wrap or transfer the salad to an airtight container. Refrigerate for at least 30 minutes before serving. This short chilling period allows the dressing to coat the pasta more evenly and helps the lemon, dill, and garlic flavors develop. Avoid leaving the salad at room temperature during chilling or preparation breaks.

Remove the cucumber pasta salad from the refrigerator and stir gently. If the dressing has thickened during chilling, fold the salad to redistribute it. If it seems unusually dry, a small spoonful of sour cream can help restore its creamy texture. Taste once more and adjust the seasoning if necessary. Transfer to a serving bowl and sprinkle with the optional 1 tablespoon (3 g) fresh dill. Serve cold.