In a large mixing bowl, cream together the butter, sugar, salt, baking soda, and vanilla until light and fluffy, at least 5 minutes (don’t skimp this step!). In a separate bowl, whisk together the flour and cocoa. If lumps remain, sift the mixture.
Add the eggs to the butter mixture one at a time, beating well after each addition. Slowly blend one third of the flour mixture into the creamed mixture, then half the milk, another third of the flour, the remaining milk, and the remaining flour. Be sure to scrape the sides and bottom of the bowl occasionally throughout this process.
Grease and flour two 9-inch round cake pans, two or three 8-inch round pans, or a 9 X 13-inch sheet cake pan (I used two 9-inch rounds and also put a circle of parchment paper on the bottom to ease in flipping).
Divide the batter evenly between the pans. Bake the cakes for 30 to 35 minutes (test after 28 minutes – don’t overbake!).
Remove the cakes from the oven, cool them for 5 to 10 minutes, then remove from the pan.
Notes
Weigh the Ingredients: I always, always weigh my ingredients if I have the option – which I did with this cake. If I would have gone off measurement alone (I conducted a little experiment), I would have added nearly 3/4 cup too much flour!