Preheat the oven to 325 degrees F. Prepare three 8-inch or four 6-inch round cake pans by spraying the bottom and sides with nonstick spray, lining the bottom with parchment paper, and spraying the parchment paper.
In a bowl of electric mixer, combine all the dry ingredients.
Combine eggs, buttermilk, water, oil and vanilla in a measuring cup and lightly beat with a fork.
Add wet ingredients to the dry ingredients, and mix on low speed until combined. Batter will be thin. Scrape sides and mix for another 30 seconds. Divide batter evenly among prepared pans (I like to use a kitchen scale to ensure the batter is evenly distributed - about 15 to 16 ounces in each 8-inch or 12 ounces in each 6-inch).
Bake for 23 top 27 minutes (you may need more time depending on your oven), until toothpick comes out with just a few moist crumbs on it. Cool on wire racks for 10-15 minutes, then gently invert onto racks until cooled completely.
When cakes are completely cooled, I like to wrap each cake layer individually with plastic wrap and stick it in the refrigerator or freezer until I’m ready to frost. The cake will be easier to work with if it’s cooled a bit. If I’m making the cake a day or two before I actually need to frost it, I put it in the freezer to ensure freshness. If I’m frosting same-day, I’ll just put it in the refrigerator to chill until needed.