In a large mixing bowl, whisk together the mayonnaise, sour cream, and cider vinegar until smooth and well combined. Add the dill, salt, black pepper, granulated sugar, and dry mustard powder, whisking until the spices are evenly distributed throughout the dressing. This creates a flavorful base that will coat all the salad components. I like to taste the dressing at this point and adjust the vinegar or salt if needed—it should have a nice tangy, savory flavor with just a hint of sweetness.

While the dressing is ready, cook the bacon in a skillet over medium-high heat until it's golden brown and crisp, about 8-10 minutes depending on thickness. Transfer the cooked bacon to a paper towel-lined plate to drain and cool slightly, then crumble it into bite-sized pieces. This can be done while you prep the other ingredients to save time.

Add the thawed peas, cheddar cheese cubes, and finely diced red onion to the dressing from Step 1, stirring gently but thoroughly to coat everything evenly. Fold in the crumbled bacon from Step 2 at the end, being careful not to break the bacon pieces too much. I find that folding rather than stirring vigorously helps keep the texture nice and prevents the cheese from breaking down. The salad should look colorful and creamy at this point.

Transfer the salad to a serving bowl and refrigerate for at least 1 hour before serving. This chilling time allows the flavors to meld together and gives the peas and cheese time to absorb the creamy dressing. Stir gently once more before serving to redistribute any dressing that may have settled to the bottom.