Preheat oven to 425°F
Lightly grease a rimmed baking sheet with olive oil or line with parchment paper or a silicone baking mat
Place potatoes, 2 tablespoons olive oil, rosemary, and garlic in a bowl and toss to combine
Add sea salt and black pepper
Layer potatoes on the baking sheet in a single layer
Roast in preheated oven for 15 minutes
Gently toss potatoes to help them brown evenly and return to the oven
Roast for another 10-15 minutes, potatoes should be fork-tender
While potatoes are roasting, add onions and 2 tablespoons olive oil to a large skillet
Sautee over medium heat, stirring occasionally, until they turn golden brown, about 10 minutes
Remove onions from heat
Place roasted potatoes and sauteed onions in a large bowl and toss to combine
Add extra sea salt and pepper if neededServe immediatelyEnjoy!