Preheat oven to 350°F and line a 6-muffin tin with paper cupcake liners.
In a measuring cup, whisk together the milk and apple cider vinegar. Set aside.
In a medium mixing bowl, stir together the flour, cornstarch, baking powder, baking soda, and salt. Set aside.
Into a large mixing bowl, add the butter and sugar. Using a handheld mixer on medium speed, mix for 1 minute, until light and fluffy.
Mix in the vanilla and almond extracts.
Add 1/2 of the oat milk mixture and 1/2 of the flour mixture. Continue mixing to combine.
Add the remaining milk and flour mixtures, mixing just until fully incorporated. Do not overmix the batter; this collapses the bubbles in the batter and can lead to denser cupcakes.
Pour batter evenly into the cupcake liners.
Bake for 20 minutes, until a toothpick inserted into the center of one of the cupcakes comes out clean. Transfer to a cooling rack and let the cupcakes cool completely before frosting.