Boil the macaroni and the potatoes in two separate pots simultaneously. Cook the macaroni until it’s fully softened—not necessarily al dente. Cook the potatoes until fork tender. In a separate bowl, mash the potatoes into a coarse mash. It should be about half chunky and half smooth.
Next, mix the dressing: add the mayonnaise, milk, cider vinegar, and sugar.
In a large bowl, mix the boiled macaroni with the peas, carrots, and grated onion. Pour the dressing in. Mix thoroughly. Now add the mashed potatoes. Add salt to taste.
