1) Preheat the oven to 350°F. Grease and flour three 8" or two 9" round cake pans.
2) Beat the butter, sugar, and vanilla extract (or fruit zest) into a smooth paste. The sugar will stay granular.
3) Add the eggs one at a time, beating at medium speed just until they're incorporated, and scraping the bottom of the bowl after each addition.
4) Add the flour alternately with the milk, mixing at medium-low speed and beginning and ending with the flour. Scrape the bowl a few times during this process. Once the last of the flour is added, mix briefly, just until smooth.
5) Divide the batter between the pans. Cakes will self-level in the oven, so there's no need to smooth the top with a spatula. However, it does help to remove any large bubbles by banging the cake pans firmly on the counter 7 or 8 times.
6) Bake the cakes for 30 to 35 minutes, until evenly browned and a cake tester inserted into the center of one comes out clean.
7) Remove from the oven, and cool in the pan for 5 minutes. Run a spatula around the edges to loosen, and turn out onto a rack to cool completely before frosting.
Yield: 2 round 9" layers or 3 round 8" layers.