The Method
1. Prep with Precision
Preheat your oven to 200°C (400°F). Scrub your potatoes and cut them into uniform 1-inch cubes. If they are too large, they won’t soften by the time the onions caramelize; too small, and they’ll turn to mush. Peel your onions and slice them into thick half-moons.
2. The Toss
In a large mixing bowl (or directly in your roasting tin if you want to save on washing up), toss the potatoes and onions with a generous glug of olive oil. Season heavily with salt and pepper. You want every single surface glistening with oil and speckled with seasoning.
3. The Roast
Spread the mixture in a single layer. This is crucial—if the pan is crowded, the vegetables will steam instead of roast. Slide them into the oven for 45 to 55 minutes.
4. The Flip
Halfway through, use a sturdy spatula to flip the potatoes. This ensures the underside gets that deep, dark crust. You’ll know they are done when the onions are shriveled and dark brown, and the potatoes offer no resistance to a fork.
Pro-Tips for Perfect Results
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The “Crowding” Rule: If you’re doubling the recipe, use two separate sheet pans. A crowded pan is the enemy of the crunch.
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High Heat is Key: Don’t be afraid of the “burnt” looking bits on the onions. That is where all the concentrated sweetness lives.
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Add a Herb Kick: If you want to break the “4-ingredient” rule once you’ve mastered the base, a sprig of fresh rosemary or thyme tossed in at the beginning adds a wonderful woody aroma.
A Note on the Pan: Using an older, well-seasoned metal roasting tin (like the one in the photo) actually helps with heat distribution and browning compared to glass or ceramic dishes.
