Ingredients
2 pounds russet or yellow potatoes, scrubbed and cut into 1-inch chunks
2 large yellow onions, peeled and sliced into thick half-moons
4 tablespoons unsalted butter, melted (plus a little extra for greasing the pan)
1 1/2 teaspoons kosher salt (or to taste)
Directions
Preheat your oven to 400°F (200°C). Lightly grease a metal baking pan (an 8×11 or 9×13 works well) with a small pat of butter so the potatoes and onions don’t stick and can really crisp and caramelize.
Prep the potatoes by scrubbing them well and cutting them into roughly 1-inch chunks so they cook evenly. If you’re short on time, you can leave the skins on for extra texture and less prep.
Slice the onions into thick half-moons so they hold up in the oven. Aim for about 1/2-inch thickness; thinner slices will burn before the potatoes are tender.
Add the potato chunks and onion slices to the prepared baking pan, spreading them out in as even a layer as you can. A little overlap is fine, but try not to pile them too deep or they’ll steam instead of roast.
Drizzle the melted butter evenly over the potatoes and onions, then sprinkle the kosher salt over the top. Use clean hands or a large spoon to toss everything right in the pan until every piece looks lightly coated in butter and seasoning.
Spread the mixture back into an even layer, making sure plenty of onion slices are nestled down between the potatoes so they can soften and caramelize together.
Place the pan on the middle rack of the preheated oven and bake for 25 minutes without stirring, letting the bottoms start to brown and the onions begin to soften.
After 25 minutes, carefully remove the pan and give everything a good toss, scraping up any golden bits from the bottom of the pan. Spread back into an even layer and return to the oven.
Continue roasting for another 20–30 minutes, stirring once or twice, until the potatoes are tender all the way through, the edges are deeply golden, and the onion slices are soft, sweet, and caramelized in spots. Total time will be about 45–55 minutes depending on your oven and the size of your potato chunks.
Taste and add a pinch more salt if needed. Serve the potatoes and onions hot, straight from the pan, making sure to scoop up the caramelized onion bits and buttery drippings from the bottom.
Variations & Tips
For a slightly richer version, dot an extra tablespoon or two of butter over the top during the last 10 minutes of baking so it melts into the potatoes and onions. If you like a bit of color, you can use a mix of red and yellow potatoes, or swap in sweet onions for an even more caramelized flavor. To stretch the recipe for a bigger crowd, add up to 1 extra pound of potatoes and 1 more onion, then increase the butter and salt slightly and use a larger pan so everything can still roast, not steam. If you’re prepping ahead on a busy day, you can cut the potatoes and onions in the morning, toss them with melted butter and salt, cover, and refrigerate right in the pan; just give them a quick toss and roast as directed, adding 5–10 extra minutes if they’re going into the oven cold. For crisper edges, roast on a lower rack and don’t overcrowd the pan; for softer, more casserole-style potatoes, cover the pan loosely with foil for the first 20 minutes, then uncover to finish browning.