Bring 4 quarts water and 1 tablespoon salt to boil. Add pasta and cook until al dente, about 6 minutes. Drain well and rinse under cold water.
To make the custard:
Meanwhile, in a medium saucepan over medium heat, whisk together sugar, flour, 1/2 teaspoon salt, pineapple juice, and eggs.
Cook until thickened, stirring occasionally, about 10 minutes. Remove from heat, add lemon juice, cover, and chill at least 30 minutes.
To assemble the salad:
In a large bowl, combine the pasta, custard, mandarin oranges, pineapple, and whipped topping. Mix well and refrigerate at least 30 minutes or overnight. Before serving, add marshmallows and coconut and toss to combine.
Notes
Acini di pepe: For the best texture, cook until al dente, about 6 minutes in boiling, salted water, and chill immediately. If you can’t find acini di pepe, substitute it with another small-cut pasta such as pastina or small stars, Israeli-style couscous, or even tapioca pearls. Keep in mind that cooking times may vary.
Crushed pineapple: You'll want one 20-ounce can. Drain the liquid from the fruit, then use that liquid as the start of the 1 3/4 cup pineapple juice required for the custard.
Frozen whipped topping: If you're not a fan of frozen whipped topping (Cool Whip), feel free to make homemade Whipped Cream. In a large bowl, pour in 1 1⁄2 cups heavy whipping cream and whisk until stiff peaks form, making about 3 cups.
Shredded coconut: The traditional recipes always use sweetened coconut, but I've made it with unsweetened coconut and it's great! To bring out the nutty, tropical flavors even more, toast the coconut before adding it to this Frog's Eye Salad recipe.
Yield: My Frog's Eye Salad recipe makes about 24 side dish or dessert servings.
Storage: Store leftovers covered in the refrigerator for up to 4 days.