Cook pasta for 12 minutes; then drain. (I add a bit of vegetable oil to the water before it comes to a boil, so pasta doesn't stick together).
Rinse pasta under cold water, and drain pasta well.
In a large bowl mix together, the sweetened condensed milk, mayonnaise, sugar, vinegar, buttermilk, salt and pepper.
Place in refrigerator til ready to mix salad ingredients together.
When ready to assemble salad together, in a medium sized bowl, add some of the pasta, some of the carrots, a teaspoon or so of the diced red onion, a third of the diced celery, and some of the dressing; mix together gently with a spatula.
Add salad mixture to a "very" large size bowl, (I used my largest Tupperware bowl; total capacity: 32 cups) cuz this recipe does make an enormous amount of salad.
Toss a few peas, over the salad.
Repeat mixing the pasta, carrots, onion and celery together, (in small amounts) in the medium sized bowl along with the dressing, then place ontop of the salad in the "very" large size bowl, along with some of the peas.
Keep layering til all the ingredients are used up; ending with peas ontop of the salad.
Cover the bowl, and chill salad for several hours in the refrigerator, or overnight.
Before serving, be sure to stir the salad.
This salad keeps well for several days in the refrigerator.
Note: For this recipe, I substituted matchstix (French-Cut Cooking Carrots) for the shredded carrots. You can find these in your produce section. It came in a (10 oz.) bag, but I only use 3/4's of the bag, about (8 oz).