Chocolate Skillet Cake with Ice Cream

Cak ingrédients

1 cup flour
1/2 teaspoon baking soda
1 cup sugar
dash salt
1/4 cup (1/2 stick) butter
1/4 cup vegetable oil
2 tablespoons cocoa powder
1/2 cup water
1/4 cup buttermilk
1 egg
1/2 teaspoon vanilla