Take the softened butter and evenly grease a 10 inch cast iron skillet or baking pan (it can be a 8 x10 inch or similar)
To replace buttermilk, just add 1 tbsp of white vinegar to 1 cup of milk and let sit for about 5 minutes. It will sour perfectly
You can bake up this batter as muffins as well. It will fill about 12 regular sized muffins. Give them about 15-20 minutes in the oven, but check at the 15 minute mark.