Place a metal or glass mixing bowl and the mixer beaters in the refrigerator or freezer for 10–15 minutes. Chilled tools help the heavy cream whip faster and thicker.
Pour the cold heavy whipping cream into the chilled bowl. Beat on medium-high speed until it starts to thicken, then sprinkle in the powdered sugar and vanilla. Continue beating until soft to medium peaks form—billowy and smooth, not stiff or grainy.
1 cup heavy whipping cream, 3 tablespoons powdered sugar, 1 teaspoon vanilla extract
Add the sour cream to the whipped cream. Gently fold with a spatula until smooth and fully combined. Taste and add 1–2 more tablespoons of powdered sugar if you prefer a sweeter cream. Chill this creamy base in the refrigerator while you prep the fruit.
1 cup sour cream
Drain the pineapple tidbits and mandarin oranges very well. Press them lightly with paper towels to remove excess juice. Halve the grapes, chop the nuts if using, and drain and pat the maraschino cherries dry. The drier the fruit, the fluffier and less runny the salad will be.
1 can (20 oz) pineapple tidbits, 1 can (15 oz) mandarin oranges, 1 cup seedless grapes, 1/2 cup pecans or walnuts, 1/2 cup maraschino cherries
In a large mixing bowl, add the pineapple tidbits, mandarin oranges, halved grapes, halved cherries, mini marshmallows, shredded coconut, and chopped nuts (if using). Sprinkle in a pinch of salt. Gently toss until everything is evenly distributed, taking care not to break up the orange segments.
1 can (20 oz) pineapple tidbits, 1 can (15 oz) mandarin oranges, 1 cup seedless grapes, 1 1/2 cups mini marshmallows, 1 cup sweetened shredded coconut, 1/2 cup pecans or walnuts, 1/2 cup maraschino cherries, salt
Spoon the whipped cream–sour cream mixture over the fruit mixture. Using a large spatula, gently fold from the bottom of the bowl up, turning the bowl as you go, until all the fruit is coated and no large streaks of cream remain.
Cover the bowl tightly with plastic wrap or a lid. Refrigerate for at least 2 hours and up to 8 hours. This resting time allows the flavors to meld and the marshmallows to soften so the salad becomes fluffy and spoonable.
Before serving, give the ambrosia salad a gentle stir. Transfer to a serving bowl if desired and garnish with a sprinkle of shredded coconut, a few extra maraschino cherries, and additional chopped nuts. Serve well chilled.