Preheat oven to 350 degrees F. In a bowl whisk together dry ingredients of flour, salt and baking powder and set aside.
Use a stand mixer to beat the softened butter for about 1 minute, then add white sugar and beat for a few more minutes until it reaches a fluffy texture
Add eggs one at a time, continuing to beat together. Then add yolks one at a time mixing again. Add vanilla and yogurt or sour cream. Mix. Pour in half of your dry ingredients and mix again.
Add milk, mix and then add in remaining dry ingredients. Mix until you achieve a smooth batter. Cut a piece of parchment paper to fit into the bottom of your 8" pan(s). Pour batter inside pan(s)
If you are using 1 8x3" pan, fill to 3/4 of the way full and bake for 55-60 minutes, if using 2 - 8" pans divide evenly between them and bake for 23-28 minutes or until toothpick in the center of cake(s) comes out clean and golden brown on top.
Remove and set on cooling rack for at least 15 minutes and until cool enough to lift pan, use a knife to loosen sides, and remove from pan(s). Set on cooling rack until completely cooled if you want to frost.