Prepare three 8 inch cake pans with parchment paper circles in the bottom and grease the sides. Leave the oven at 350°F (176°C).
In a large mixing bowl, cream the butter and sugar together until light in color and fluffy, about 3-4 minutes. Do not skimp on the creaming time.
Add the sour cream and vanilla extract and mix until well combined.
Add the eggs one at a time, mixing until combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
Combine the dry ingredients in a separate bowl, then combine the milk and water in a measuring cup.
Add half of the dry ingredients to the batter and mix until well combined. Add the milk mixture and mix until well combined. Add remaining dry ingredients and mix until well combined. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
Gently stir 1 cup of the toasted pecans into the batter.
Divide the batter evenly between the cakes pans and bake for about 24-26 minutes, or until a toothpick comes out with a few crumbs.
Remove the cakes from the oven and allow to cool for about 2-3 minutes, then remove to cooling racks to cool completely.