Step 1: Prepare the Potatoes - Cut the baby potatoes into bite sized pieces that are as even as you can reasonably make them. You do not need to pull out a ruler or make this a project. Just aim for pieces that will cook at about the same speed and sit comfortably on a fork. Place the potatoes in a large pot, then cover them with cold water by about an inch. Starting with cold water helps the potatoes cook evenly from the center to the outside.
Step 2: Boil Until Fork Tender - Set the pot over medium high heat and bring the water to a boil. Once it is boiling, cook the potatoes for about 12 to 15 minutes. Check a larger piece by sliding a fork into the center. The fork should go in easily, but the potato should not crumble apart. You want tender potatoes that can absorb some dressing while still holding their shape when the salad is stirred.
Step 3: Drain and Cool the Potatoes - Pour the potatoes into a colander and let all the hot water drain away. Leave them there for several minutes so excess steam can escape. This small pause matters because very hot, wet potatoes can make the dressing loose or oily. They do not need to become completely cold, but they should be only slightly warm before you add them to the creamy mixture.
Step 4: Whisk the Ranch Dressing - In a large mixing bowl, add the mayonnaise, sour cream, ranch seasoning mix, garlic powder, salt, and black pepper. Whisk until the mixture is smooth and no streaks of sour cream remain. Give it a quick taste with a clean spoon. It should taste a little stronger and saltier than you might expect because the potatoes will soften the seasoning once everything is combined.
Step 5: Coat the Potatoes Gently - Add the slightly cooled potatoes to the bowl of ranch dressing. Use a large spoon or flexible spatula to fold everything together, lifting from the bottom of the bowl rather than stirring aggressively. Continue until every potato is covered in a creamy layer. A few soft edges may break off and thicken the dressing, which is completely fine, but you still want most of the pieces to remain intact.
Step 6: Add the Cheddar and Green Onions - Sprinkle in the shredded cheddar cheese and chopped green onions. Fold them through the salad gently so they are spread evenly from top to bottom. Freshly shredded cheese blends into the dressing more smoothly than packaged cheese, but either will work when dinner needs to happen and you are using what is already in the refrigerator.
Step 7: Chill the Potato Salad - Cover the bowl tightly and place it in the refrigerator for at least 2 hours. This resting time lets the potatoes cool fully and gives the ranch, garlic, cheddar, and green onion flavors a chance to settle into one another. The salad will also become thicker as it chills. I usually use this time to clean the kitchen, get the rest of dinner ready, or enjoy the rare moment when one part of the meal is already finished.
Step 8: Fold in the First Layer of Doritos - Just before serving, lightly crush the Cool Ranch Doritos with your hands while they are still in the bag, or place them in a large food storage bag and press gently. Keep a mixture of medium and small pieces. Fold about half of the crushed chips into the chilled potato salad. Use only a few slow turns of the spoon so the chips stay as crisp as possible.
Step 9: Finish and Serve - Spoon the potato salad into your serving bowl, then scatter the remaining crushed Doritos over the top. Finish with extra chopped green onions for color and freshness. Serve it immediately while the top layer is loud and crunchy. That first spoonful, with cold ranch coated potato underneath and crisp chips on top, is exactly why this salad disappears so quickly.