Preheat oven to 425 F and line baking sheet with aluminum foil.

Prick potatoes all over with fork. Bake until potatoes are tender and fork inserted easily comes out, 45 minutes-1 hour. Split tops of potatoes open with knife and fluff potato flesh with fork. Set aside.

In small bowl, combine sour cream and milk, adding more milk as needed, until sour cream is pourable. Set aside.

In large skillet or on griddle over medium-high heat, heat 1 tablespoon butter. Add peppers and onions; cook until tender, 3-4 minutes. Season with salt and pepper, to taste. Transfer to plate and set aside.

Clean skillet then melt remaining butter. Add steak and cook until fully cooked and lightly browned, 3-4 minutes. Season with salt and pepper, to taste. Return vegetables to skillet and toss to combine.

Evenly top each potato with 1 tablespoon butter, steak mixture and cheese. Transfer to oven and bake until cheese is melted, 2-3 minutes. Drizzle with sour cream and serve.