Preheat oven to 350°
In a 10" cast iron skillet, spray with a baking spray or use a little shortening or oil rubbed on bottom and sites so the cake comes out easily.
In a larger bowl (with a mixer or whisk) beat the butter and sugar until fluffy.
Add in eggs one at a time mixing each well.
Mix in vanilla.
Mix the flour with baking soda, then add half the flour mixture.
Add in the buttermilk and mix well.
Then add in the remaining flour mixture and continue mixing until the batter is creamy and well blended.
Pour the batter into a 10" skillet and bake at 350° for 30 minutes or until a toothpick comes out clean.
Allow cake to cool at least 15 minutes, if you want to serve it warm or cool completely.
If you put the icing on a warm cake it will be thin, but taste amazing.