Cook bacon in a 9" cast iron skillet on the stove over medium-high heat until cooked. Turn off stove; remove bacon and pour off all but 1 tablespoon of bacon grease in the skillet. Chop bacon into small pieces.
In a large bowl, stir the cornmeal, salt and baking soda together. In a separate bowl, stir pureed sweet potato, buttermilk, and beaten eggs until thoroughly combined. Stir in chopped bacon. Add sweet potato mixture into the cornmeal mixture and stir until combined.
Pour batter into skillet and bake in the preheated oven until top of cornbread is brown and it feels firm to the touch, about 30 minutes. Turn out on to a serving plate. Cut into wedges and serve immediately with butter.