Preheat the oven to 350°F (180°C) and line the muffin pan with 6 cupcake liners. Set aside.

In a medium-size bowl, using a whisk, combine all-purpose flour, cornstarch, baking powder, baking soda, ground cinnamon, nutmeg, and a pinch of salt. Set aside.

In a large bowl using a hand mixer or a stand mixer, beat vegan butter with granulated sugar on high speed until fluffy and lighter in color for about 3-4 minutes. Add in vegan yogurt and mix until incorporated. Slowly and gradually mix in oat milk, vegan eggnog, and apple cider vinegar. Mix until fully combined. Then sift in dry ingredients and gently combine using a spatula.

Divide the batter evenly into 6 cupcake liners. Bake in preheated oven for 20-25 minutes or until a toothpick inserted into the middle comes out clean. If it looks wet, bake for about 5 minutes longer.

Transfer to a cooling rack and allow to cool completely before frosting.

Add soft vegan butter to a large bowl (alternatively, add the vegan butter to a stand mixer with the whisk attachment) and cream with a hand mixer on high speed until fluffy and lighter in color for about 2-3 minutes. Sift in powdered sugar and mix until combined. Slowly and gradually mix in vegan eggnog until incorporated and fluffy. Lastly, mix in vanilla and ground nutmeg.

Using a piping bag with a star tip, pipe a swirl of frosting onto each cupcake. Top with a sprinkle of nutmeg or cinnamon.