Preheat your oven 375℉/190℃

Soak the potatoes and onion: Cut the russet potatoes into inch-sized cubes and place them in a large bowl filled with cold water. Then cut up the sweet potatoes and onion into inch-sized cubes and place them in a separate large bowl filled with cold water.

Prep the potatoes: Drain off the water from the bowl with potatoes. Transfer them to a layer of paper towels and pat them dry. Dry the bowl and return the potatoes to it. Pour in 1½ Tablespoons of oil along with ½ teaspoon each of salt, pepper, rosemary, oregano, and smoked paprika. Toss this so that all of the potatoes are coated in oil and spices. Transfer the potatoes to a foil-lined baking sheet making sure to leave an oval at the center.

Place the potatoes in your heated oven and let them bake for 15 minutes.

Prep the sweet potato and onion: While the potatoes are baking drain off the water from the bowl with the sweet potato and onion. Transfer the sweet potato and onion to paper towels and pat them dry. Dry the bowl and return the sweet potato and onion to it. Pour in 1 Tablespoon of oil, along with ¼ teaspoon each of salt, pepper, rosemary, oregano, and smoked paprika. Then toss so that everything is coated in oil and spices.

After 15 minutes take the potatoes out of the oven and use a spatula to turn them over. Put them back to the outside and add the sweet potatoes and onion to the center.

Finish roasting everything: Place this back in the oven and let everything roast for 30 to 45 minutes. Make sure to flip and mix everything with a spatula every 10 to 15 minutes. You will know that the roasted potatoes are done when everything is tender, and the outsides have become golden brown & crispy. In the end, you can add more salt & pepper if you feel like it’s needed.

Take the roasted potatoes out of the oven, transfer them to a serving bowl, and enjoy!