Everyone thinks they know how to cut a potato. You grab a knife, you hack it into chunks, you throw it in the oven, and you hope for the best. Usually, you end up with something that’s okay—maybe a bit soft on one side, maybe a little burnt on the points—but it’s rarely that glass-shattering, golden-brown perfection you see in high-end gastropubs.
The secret isn't just the oil or the heat. It’s the geometry.
How you cut potatoes for roasting determines exactly how much surface area comes into contact with the hot fat and the roasting pan. If you've been doing simple cubes, you're leaving flavor on the table. You're basically settling for "fine" when you could have "incredible." Let’s get into why your current knife skills might be holding back your Sunday roast and how a few specific angles can change everything.
The Science of Surface Area and Starch
If you talk to any serious chef, like Kenji López-Alt from Serious Eats, they’ll tell you that roasting is a battle for surface area. You want as many flat, craggy edges as possible. Why? Because that’s where the Maillard reaction happens. This is the chemical dance between amino acids and reducing sugars that gives roasted food its brown color and distinctive savory flavor.
A cube has six sides. A rough-cut wedge or a "seven-sided" roast potato has significantly more. When you increase the surface area relative to the volume of the potato, you increase the potential for crunch.
It's also about the starch. When you cut a potato, you’re rupturing cells and releasing starch. If you cut them too small, they turn into mush before the outside gets crispy. If they're too big, the middle stays dense and waxy. Finding that middle ground—roughly two-inch chunks—is the sweet spot for a fluffy interior and a tectonic exterior.
Stop Making Perfect Cubes
Standard cubes are for hash browns, not for roasting. When you cut a potato into a perfect square, it sits flat on the pan. Only one side gets that direct heat contact at a time. It’s boring.
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Instead, try the oblique cut or the "roll cut."
Hold your potato at an angle and slice off a piece. Then, roll the potato 90 degrees and slice again at the same angle. You’ll end up with these irregular, triangular shapes that look like something out of a geology textbook. These shapes are brilliant because they have sharp, thin edges that crisp up almost instantly, while the thicker centers stay creamy. It’s a texture contrast that a cube just can't provide.
I’ve seen people spend forty minutes obsessing over the type of salt they use while ignoring the fact that their potato chunks are all different sizes. That’s a mistake. While you want irregular shapes, you want consistent mass. If one piece is the size of a marble and the other is the size of a lemon, the small one will be charcoal by the time the big one is edible. Aim for chunks that are roughly 1.5 to 2 inches across.
The Best Potatoes for the Job
You can't talk about cutting without talking about what you're cutting.
- Russets: These are the high-starch kings. Because they’re so floury, the edges break down easily when you parboil them (more on that in a second). This creates a "mash" on the surface that fries in the oven fat.
- Yukon Golds: These are the all-rounders. They have a buttery flavor and hold their shape better than Russets. If you like a "creamy" roast potato, go for these.
- Red Potatoes: Honestly? Just don't. They’re too waxy. They’re great for potato salad, but for roasting, they’ll never give you that deep, thick crust you’re looking for.
The Pre-Cut Ritual: To Peel or Not?
Peeling is a personal choice, but if you’re looking for the definitive "roast potato" experience, you’ve got to lose the skin.
Potato skin is a barrier. It prevents the fat from interacting directly with the starch of the potato flesh. If you leave the skin on, you’re basically steaming the potato inside its own jacket. It’s tasty, sure, but it’s not roasting in the purest sense. By peeling the potato before you cut it, you expose the entire surface to the roasting environment.
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If you’re doing a quick weeknight meal, skin-on wedges are fine. But if you’re trying to win at dinner, peel them. Use a sharp Y-peeler—it’s faster and safer than the old-school swivel peelers.
How to Cut Potatoes for Roasting: The Step-by-Step Breakdown
- Halve them lengthwise. Start with a clean, peeled potato. Slice it right down the middle the long way.
- The Angled Approach. Instead of cutting straight across into half-moons, tilt your knife at a 45-degree angle.
- The "V" Cut. Slice into the potato at that angle, then flip the knife's direction for the next cut. You're essentially cutting out wedges, but by rotating the potato as you go, you create more facets.
- Size Check. If you have a massive Russet, you might need to quarter it lengthwise first before you start making your chunks.
Think of it like cutting a diamond. Every extra face you add to that potato is another opportunity for a golden, crunchy crust.
Why Parboiling Changes the Surface
Once you've mastered how to cut potatoes for roasting, you have to treat the surface. This is the part people skip because they’re in a hurry. Big mistake.
Drop those angled chunks into a pot of cold, heavily salted water. Add a half-teaspoon of baking soda. This is a trick popularized by J. Kenji López-Alt. The baking soda breaks down the potato’s pectin, drawing more starch to the surface.
Boil them until the edges are soft. We're talking "almost falling apart" soft. Drain them, let the steam escape for a minute, and then—this is the fun part—shake the hell out of the pot.
By shaking the pot, you’re scuffing up those beautiful edges you just cut. You’re creating a layer of potato "fuzz." When that fuzz meets hot oil in the oven, it dehydrates and browns into a thick, crunchy shell that stays crispy even after the potato starts to cool down.
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Common Mistakes to Avoid
- Crowding the Pan: If your potatoes are touching, they're steaming. Give them space. Use two pans if you have to.
- Using Too Little Fat: You aren't just baking these; you're shallow-frying them in the oven. You want enough oil (or duck fat, if you're feeling fancy) to coat every single one of those jagged edges.
- Cold Pans: Put your roasting pan in the oven while it preheats. When you dump the potatoes onto a screaming hot pan, they start searing immediately.
- Too Much Flipping: Let them sit. They need time to develop a crust. If you flip them every ten minutes, you’ll break off those delicate, crispy bits you worked so hard to create.
Beyond the Basic Wedge
If you're bored of the "chunk" look, there are two other ways to cut potatoes for roasting that offer different experiences.
The Hasselback Cut: This involves slicing thin slits into the potato, but not all the way through. It looks like an accordion. It’s visually stunning and creates a lot of crispy edges, but the bottom can sometimes stay a bit soggy if you aren't careful. Use a pair of chopsticks on either side of the potato to act as "stops" so your knife doesn't go all the way to the board.
The Smashed Potato: You boil small, whole potatoes until tender, then use a heavy glass to "smash" them flat on a baking sheet. This creates a massive amount of surface area and a very thin, cracker-like potato. It’s technically a roast potato, but the ratio of crunch-to-fluff is heavily skewed toward the crunch.
Final Actionable Steps for Perfect Potatoes
To get the best results tonight, follow this exact workflow.
First, choose a starchy potato like a Russet or Maris Piper. Peel them completely. Cut them into irregular, 2-inch chunks using angled, non-parallel cuts to maximize surface area.
Second, boil the chunks in alkaline water (water plus baking soda) until the exteriors are fuzzy and soft. Drain them and shake the pot vigorously to roughen the edges.
Third, preheat a heavy-duty roasting pan with plenty of high-smoke-point fat—like beef tallow, duck fat, or avocado oil—at 425°F (220°C). Carefully toss the potatoes in the hot fat and spread them out so no two pieces are touching. Roast for at least 45 to 55 minutes, turning only once or twice, until they look like deep-orange nuggets of gold.
Finish with flaky sea salt and fresh rosemary while they’re still screaming hot. You’ll never go back to basic cubes again.