Set the air fryer to Bake at 360˚F. Butter and flour two 4-inch cake pans. In a medium bowl, sift together the flour, salt, and baking soda. In the bowl of a stand mixer, cream the butter on medium speed until smooth and lump free. Add in sugar and mix on medium until light and fluffy. Scrape the sides with your spatula and add eggs in one at a time. Repeat and scrape the sides and add in vanilla paste. Sift the cocoa and espresso powder into the butter mixture and combine. Scrape the sides of the bowl. In a separate bowl, mix together the buttermilk, vinegar, and red food coloring. (Not required to use all red food coloring. Add red coloring according to your preference.) Alternate adding dry mix and liquid mix into butter mixture. Starting with adding half the dry mix. Ensure to scrape down the bowl occasionally. Divide the batter among the prepared pans. Place one pan in the air fryer and bake for 15-18 minutes or until a toothpick comes out clean or the cake springs back to the touch. Once fully baked, repeat this step with the second pan. Let the cake pans cool for 10-15 minutes, then turn them out onto a wire rack to cool completely. Frost with your favorite Swiss meringue cream cheese buttercream frosting.