For the Cake

1. Preheat the oven to 350°F and set an oven rack in the middle position. Butter and flour a 9x13-in pan, or use nonstick cooking spray with flour in it, such as Baker's Joy or Pam with Flour.
2. In a medium bowl, whisk together the flour, salt and baking soda. Set aside.
3. In the bowl of an electric mixer fitted with the paddle attachment (or beaters), beat the butter and sugar on medium speed until light and fluffy, about 5 minutes. Beat in the vanilla, then beat in the eggs, one at a time, scraping down the sides of the bowl as necessary. (Don't worry if the batter looks a little curdled at this point.)
4. Reduce the speed to low, then beat in one-third of the flour mixture, followed by half of the buttermilk. Scrape down the sides and bottom of the bowl, then add another third of the flour, followed by the remaining buttermilk. Beat in the remaining flour, then scrape down the bowl and beat again until the batter is evenly combined. Do not overmix.
5. Scrape the batter into the prepared baking pan and bake for 30 to 35 minutes, until the cake is set and lightly golden around the edges, and a toothpick inserted into the center comes out clean. Set the cake on a wire rack to cool completely.

For the Frosting

1. In the bowl of a stand mixer fitted with the paddle attachment (or beaters), combine the cream cheese, butter, vanilla and salt. Mix on low speed until combined, then increase the speed to medium-high and beat until aerated and light, about 2 minutes. Stop the mixer and add about half of the confectioners' sugar; mix on low to combine. Gradually add the remaining sugar, keeping the speed on low. Once all of the sugar is mixed in, increase the speed to medium-high and beat until fluffy, about 1 minute.
2. When the cake is cool, use a butter knife or small offset spatula to swirl the frosting lavishly over top. The cake is best enjoyed fresh on the day it is baked, but it will keep nicely for a few days. Store in an airtight container (or cover tightly with plastic wrap) at room temperature.
3. Note: If you’d like to make your own buttermilk, check out the easy method here.