Bake the Pastry: Prepare and bake the puff or choux pastry according to your recipe or package instructions until golden and puffed. Let it cool slightly.
Prepare the Eggnog Custard: In a saucepan over medium heat, whisk together eggs, sugar, milk, cornstarch, butter, vanilla, and a pinch of nutmeg. Cook, stirring constantly, until thickened. Remove from heat and let cool slightly.
Assemble the Cake: Slice the baked pastry and layer it in a cake dish or trifle dish with the eggnog custard. Repeat layers if desired.
Add Topping: Spread whipped cream over the top layer and lightly dust with nutmeg for garnish.
Chill: Refrigerate for at least 2 hours to allow the flavors to meld and the cake to set.
