In a medium saucepan, combine 1 cup of water, ½ cup of unsalted butter, and ¼ teaspoon of salt; bring to a gentle simmer. Add 1 cup of all-purpose flour, stirring until a ball of dough forms.

Transfer dough to a mixing bowl and let cool for 5 minutes. Beat in 4 large eggs one at a time until dough is glossy and pipeable.

Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper. Pipe mounds of dough onto the tray and bake for 25 minutes until golden. Turn off oven and leave puffs inside for 10 minutes.

In a saucepan, whisk together 1.5 cups of eggnog, ⅓ cup of sugar, 3 tablespoons of cornstarch, and ¼ teaspoon of nutmeg. Simmer while stirring until thick (about 5 minutes). Stir in ½ teaspoon of vanilla extract and cool.

Once puffs have cooled, fill them with the eggnog custard. Use a piping bag or spoon for generous filling.

Dust filled puffs with powdered sugar just before serving. Optionally drizzle with melted white chocolate.