Let the pineapple–pudding mixture sit for 3–5 minutes at room temperature so it can continue to thicken. It should look like a loose, creamy pudding with bits of pineapple throughout.
Gently fold in the thawed whipped topping. Use a spatula and a light hand, turning the bowl as you go, until the mixture is mostly uniform in color. A few streaks of white are fine and give it that homemade, slightly uneven look Nana’s always had.
Add the mini marshmallows, chopped nuts (if using), chopped maraschino cherries (if using), and a small pinch of kosher salt. Fold everything together just until the mix-ins are evenly dispersed but still visible as soft pieces throughout the salad.
Transfer the salad to a vintage-style glass bowl or any serving dish you like, smoothing the top lightly with the back of a spoon while leaving a few soft scoops and swirls on the surface for that imperfect, scooped look.
Cover the bowl tightly with plastic wrap and refrigerate for at least 2 hours, or until softly set and chilled through. The marshmallows will soften and the mixture will become fluffier as it rests.
Just before serving, uncover and, if you like, garnish with a few maraschino cherry halves or a sprinkle of chopped nuts in the center. Serve cold, scooping generous spoonfuls so you get a mix of creamy fluff and soft mix-ins in every serving.
To keep the spirit of Nana’s card while making it your own, you can play with a few gentle variations. For extra texture, fold in 1/2 to 1 cup of drained mandarin orange segments or halved green grapes; just pat them dry so they don’t water down the fluff. If you prefer a slightly less sweet version, swap half of the whipped topping for lightly sweetened whipped cream, or choose pineapple canned in juice rather than heavy syrup. For a brighter flavor, add 1 to 2 tablespoons of finely chopped fresh mint or a teaspoon of lemon or lime zest. If nuts are an issue, skip them entirely or replace them with toasted coconut flakes for crunch. You can also portion the salad into small glass dessert cups before chilling for a more composed presentation. For a firmer set (useful if it will sit out on a buffet), stir in an extra 1/2 cup of mini marshmallows and chill at least 4 hours or overnight. Leftovers keep well in the refrigerator for 2–3 days; give the salad a gentle stir before serving again to redistribute the mix-ins.