Prepare the Gingerbread Streusel by pulsing gingerbread cookies in a food processor until coarsely ground. Combine with melted unsalted butter, mix and spread on a baking sheet. Bake at 350°F for about 5 minutes or until golden brown. Cool completely.

In a small bowl, sprinkle gelatin over cold water and let it hydrate. In a saucepan, whisk together milk and eggnog, adding spices. Heat until it begins to boil, then remove from heat.

In a mixing bowl, whisk together remaining milk, egg yolks, sugar, and cornstarch until smooth. Gradually pour in the hot milk mixture, whisking continuously.

Return the mixture to the saucepan and heat, whisking until thickened, about 5-7 minutes. Remove from heat and stir in gelatin until dissolved. Strain into a bowl and cool completely.

Whip the heavy cream until stiff peaks form. Once the egg mixture is cool, gently fold it into the whipped cream.

Pipe the Eggnog Mousse into jars, layering with Gingerbread Streusel. Refrigerate for 1-2 hours to set. Garnish before serving.