Place a rack in the center of the oven and preheat the oven and preheat the oven to 350°F
Grease the pan and lightly dust them with the flour, tapping out the excess; set aside.
Place the buttermilk and baking soda in a small bowl, and whisk until the baking soda is dissolved. Add the egg yolk, vanilla, and melted butter, and whisk to combine.
Place the flour, sugar, and salt in a medium-sized bowl and whisk to blend well.
Add the buttermilk mixture and whisk just until blended and smooth. Spoon the batter into the prepared pans, dividing it evenly between the them.
Bake the cakes until a toothpick inserted into the center of one comes out clean, about 25 minutes.
Remove the pans from the oven and transfer to a wire rack to cool for 15 minutes.
Then run a thin, sharp knife around the edge of the pans and invert them to release the cakes. Place the cakes upright on the rack and let them cool completely.
The unfrosted cakes can be stored in an air tight container in the refrigerator for up to 2 days; or they can be frozen, well wrapped, for up to 1 month. Let them return to room temperature before frosting.