Toast 1 teaspoon ground nutmeg and 1/2 teaspoon ground cinnamon in a dry skillet over medium heat for 1 to 2 minutes, stirring constantly.

Pour 4 cups almond milk and 1 cup coconut cream into a large saucepan and whisk over medium heat until smooth and warmed through, about 5 minutes.

Stir the toasted spices, 1/4 teaspoon ground cardamom, and 1/4 teaspoon sea salt into the warm milk mixture, stirring for 2 minutes to incorporate.

Heat the mixture to 160–170°F, stirring occasionally, then remove from heat.

Let the mixture cool off heat for 5 minutes.

Whip 1/2 cup aquafaba in a bowl until foamy, about 3 to 4 minutes by hand or 2 minutes with an electric mixer on medium-high.

Gently fold the whipped aquafaba into the warm milk mixture, then stir in 1/3 cup maple syrup and 2 teaspoons vanilla extract until combined.

Strain the eggnog through a fine-mesh strainer into a pitcher or glass bottles for a silky texture.

Once cooled to room temperature, stir in 1/2 cup rum or bourbon if using, then refrigerate for at least 1 hour before serving.