Return the skillet to the stove over medium high heat and melt the rest of the grease. Add the onions and saute for 2-3 minutes, stirring only once or twice while they brown. Add the corned beef and saute for 2-3 minutes, breaking it up as it warms in the skillet. Add the cabbage and season with 1/2 teaspoon of salt and pepper to taste. Toss to combine and cover with lid. Let it cook until the cabbage is bright green and barely softened. Add the potatoes back in and toss to combine. Taste and adjust seasonings as needed. Enjoy!