Step 1: Prepare the Ambrosia Salad

1. Mix the Ingredients:
   • In a large mixing bowl, combine the mini marshmallows, shredded coconut, mandarin oranges, pineapple chunks, and chopped nuts.
2. Fold in Sour Cream:
   • Gently fold in the sour cream until all ingredients are evenly coated. Set the mixture aside.

Step 2: Make the Eggnog Custard

1. Whisk the Egg Mixture:
   • In a medium saucepan, whisk together eggnog, egg yolks, granulated sugar, cornstarch, vanilla extract, and ground nutmeg until smooth.
2. Cook the Custard:
   • Heat the mixture over medium heat, stirring constantly, until it thickens and coats the back of a spoon, about 5-7 minutes.
   • Remove the custard from heat and let it cool to room temperature.

Step 3: Whip the Cream

1. Beat the Cream:
   • In a mixing bowl, beat the heavy cream, powdered sugar, and vanilla extract using an electric mixer on medium-high speed. Beat until soft peaks form, being careful not to overwhip.

Step 4: Assemble the Trifle

1. Layer the Ingredients:
   • In a trifle dish or individual serving glasses, create layers of ambrosia salad, eggnog custard, and whipped cream. Repeat the layers until all ingredients are used, finishing with a layer of whipped cream on top.
2. Create a Beautiful Finish:
   • Ensure the top layer of whipped cream is smooth and inviting.

Step 5: Garnish and Serve

1. Add a Festive Touch:
   • Lightly dust the top of the trifle with ground nutmeg for a festive presentation.
2. Chill and Serve:
   • Refrigerate the trifle for at least 2 hours to allow the flavors to meld. Serve chilled and enjoy!