Preheat your oven to 400°F (200°C).
In a large bowl, combine the halved baby potatoes and sliced smoked sausage. Drizzle with olive oil, sprinkle with ranch dressing mix, salt, and pepper; toss to coat.
Spread the mixture evenly on a large baking sheet.
Roast in the preheated oven for 25-30 minutes or until potatoes are fork-tender and golden brown.
While the potatoes and sausage roast, mix the sour cream and half of the shredded cheddar cheese in a small bowl.
Once the potatoes and sausage are done, remove them from the oven and drizzle the cheese mixture over the top. Sprinkle the remaining cheddar cheese over the dish.
Return the baking sheet to the oven and bake for an additional 5-10 minutes until the cheese is melted and bubbly.
Remove from the oven and garnish with chopped green onions before serving.