In a large bowl, whisk the mustard, grated garlic, and Italian seasoning together. Add the balsamic vinegar and whisk to combine. Slowly drizzle in the olive oil while whisking constantly. Season with salt and pepper to taste. Set aside.: The aroma of freshly grated garlic will be the first thing you notice, sharp and inviting, cutting through the mellow notes of the Dijon mustard . As you whisk in a glass or ceramic bowl, you'll see the mustard break up and start to suspend flecks of seasoning, creating a speckled, flavorful base. I like to press the back of the whisk against the bowl to work the herbs into the mustard, which releases their oils and deepens the flavor. A common mistake is under-whisking, which can leave the dressing separated later, so make sure the mustard and herbs are thoroughly combined before moving on.
Bring a large pot of salted water to a boil.: When you pour in the balsamic vinegar , listen for the soft patter as it hits the bowl, and watch the liquid swirl into the mustard, bringing a glossy sheen. The vinegar brings a bright, slightly sweet acidity that wakes up the other aromatics. Whisk briskly for about ten to twenty seconds to fully integrate the vinegar so the mixture looks unified. If you skip this step or add oil too quickly, the dressing can split, creating watery pockets that will not cling to the rotini .
Cook the pasta to al dente, according to the package directions. One minute before draining the pasta, add the peas and corn to the pot with the pasta.: As you drizzle in the olive oil , you should see the mixture thicken into a cohesive emulsion, turning slightly paler and smoother. The whisking action traps tiny droplets of oil in the vinegar and mustard, which is why a steady, slow pour is essential. The resulting dressing will feel silky on the tongue and adhere to the pasta and vegetables. One pitfall here is rushing the pour, which often results in separation, so take your time and keep a steady rhythm.
Drain the pasta, peas, and corn and run them under cool water, just until they are no longer hot to the touch.: Salt brightens flavors, while freshly ground pepper adds a background warmth. Sprinkle a little, then taste, because the olives and balsamic already contribute saltiness. When seasoning, pay attention to how the vinegar sharpens and the oil smooths, adjusting the seasoning so neither element overpowers the other. Over-salting is easy to do, so err on the side of lightness and remember you can always add more later.
Add the pasta, peas, and corn to the bowl with the vinaigrette and toss to combine.: Letting the vinaigrette sit briefly lets the flavors marry, and it will feel more cohesive when you toss it with the warm pasta. You may notice the scent deepen as the herbs rehydrate slightly in the liquid. Avoid covering the bowl too tightly at this stage, because you want the aromatics to stay bright, not stewed. A common error is letting the dressing sit for hours at room temperature, which can mute freshness; for best results, use within a few hours.
Add the remaining vegetables—tomatoes, bell pepper, cucumbers, and olives. Toss to combine.: The sound of the rolling boil is a cue that the pot is hot and ready. Adding salt to the water seasons the pasta from within, so don’t skip this step. The water should taste faintly ocean like, which ensures the rotini will carry enough base seasoning. Many people under season their pasta water, leading to a bland final dish, so be generous but not excessive with salt.
Season with additional salt and pepper, if needed. Garnish with fresh basil, if desired.: Cooking to al dente means the rotini will be tender with a slight resistance in the center, which is ideal because the pasta will soften a touch more as it cools and absorbs dressing. You should see the pasta swell and the surface become slightly glossy. Overcooked pasta becomes mushy and will not provide that satisfying bite, so taste a piece a minute or two before the lower end of the package time to judge readiness.
Enjoy immediately or chill until ready to serve. This pasta salad is delicious at room temperature or cold.: Adding frozen peas and corn at this moment gently warms them without turning them to mush, preserving their pop and sweetness. You will see the bright green of the peas revive as they heat, and the kernels will glisten. A common misstep is adding frozen vegetables too early, which yields dull color and a mealy texture, so time this to the final minute.
Drain the pasta, peas, and corn and run them under cool water, just until they are no longer hot to the touch: The cold rinse stops the cooking instantly and prevents the starch from making the salad gluey. As the water runs, you will feel the temperature drop and notice the pieces separate, which keeps the salad light. Be careful not to soak them for too long, as prolonged rinsing can wash away some flavor and leave the pasta a little limp.
Add the pasta, peas, and corn to the bowl with the vinaigrette and toss to combine: When the warm pasta meets the vinaigrette, the dressing will coat each corkscrew and cling in the grooves, creating glossy, flavorful strands. Use a gentle folding motion to avoid crushing the pasta. This step distributes seasoning evenly and warms the dressing slightly, which helps flavors meld. Avoid aggressive stirring, which can break the pasta and make the texture uneven.
Add the remaining vegetables—tomatoes, bell pepper, cucumbers, and olives: Introducing the chopped tomatoes , diced bell pepper , sliced cucumbers , and olives brings in contrast in texture and temperature. The tomatoes will release tiny pockets of juice that mingle with the dressing, while the peppers and cucumbers stay crisp. Toss gently so the pieces remain intact, and be mindful that overly vigorous tossing can bruise the tomatoes .
Toss to combine: A final toss ensures each bite has a little of everything. As you fold everything together, listen for faint clinks of vegetables against the bowl, and notice the salad’s color deepen into a cohesive mosaic. If any ingredients cluster, break them up with your spoon so the seasoning is even. A frequent mistake is under tossing, leaving pockets of unseasoned pasta or vegetables.
Season with additional salt and pepper, if needed: After tasting, you may want a pinch more salt or a crack of pepper to balance the sweetness of the corn and tomatoes . Adjusting seasoning at the end allows you to calibrate for saltiness lost during boiling or rinsing. Avoid adding too much at once; small adjustments are safer and more precise.
Garnish with fresh basil, if desired: Tearing the basil leaves releases fragrant oils that perfume the entire bowl, making the salad smell as good as it tastes. Scatter the leaves on top for a bright, herbal finish. Don’t thinly slice the basil on a cutting board with a metal knife for too long, because bruising can darken the leaves and mute their aroma.
Enjoy immediately or chill until ready to serve: Served right away, the salad has a slightly warm, comforting quality, while chilling it lets the flavors meld and yields a refreshingly cool dish. Either way, the salad keeps well for a day or two refrigerated in an airtight container. Common pitfalls include leaving it out at room temperature for too long in hot weather, so refrigerate promptly if not eaten within a couple of hours.