Crispy Smashed Purple Sweet Potatoes with Miso Butter Step-by-step instructions

Before you start

Before starting, gather all ingredients and equipment. Wash the potatoes thoroughly, as the skins are left on. Bring a large pot of water to a boil. Prepare a baking sheet lined with parchment paper. Have a heavy flat-bottomed glass or potato masher ready for smashing.

Soften the butter by leaving it at room temperature for 30 minutes, or microwave in short bursts. Grate the garlic clove and set aside. Slice the scallions and measure the sesame seeds so everything is ready when the potatoes come out of the oven.

Instructions

Boil and Smash

1. 1Boil the Potatoes
   Place the Japanese purple sweet potatoes in a large pot and cover with cold water. Bring to a boil over high heat, then reduce to a simmer and cook for 20–25 minutes, until a fork slides easily into the center of a potato. Drain well and let cool for a few minutes until just cool enough to handle.
   Look for Potatoes are fork-tender but still hold their shape.
   Tip Boiling whole potatoes keeps the interior moist and prevents them from splitting.
2. 2Smash the Potatoes
   Preheat the oven to 425°F (220°C). Line a baking sheet with parchment paper. Place the boiled potatoes on the sheet, leaving space between each. Use a heavy flat-bottomed glass or a potato masher to gently press down on each potato until it flattens to about 1/2-inch thick. The edges will crack and create lacy, rough edges.
   Look for Potatoes are flattened with craggy edges and some splitting.
   Tip Don't press too hard — you want the potato to stay in one piece while creating those crispy edges.
3. 3Brush with Oil and Season
   Brush the tops of the smashed potatoes with olive oil, making sure to get into the cracks and crevices. Sprinkle evenly with sea salt. Turn the potatoes over and brush the other side with the remaining oil, then season again with a pinch of salt.
   Look for Potatoes glisten with oil and are evenly seasoned.
   Tip Using a pastry brush helps coat every surface without oversaturating the potatoes.

After boiling and smashing, the potatoes should be tender but intact, with rough, lacy edges from the pressing. They should look like flattened discs with some cracks and splits.

The interior should be a vibrant violet. Before moving on, ensure the oven is preheated and the potatoes are evenly coated with oil and salt.

Roast and Make Miso Butter

4. 4Roast Until Crispy
   Roast the potatoes in the preheated oven for 25–30 minutes, flipping halfway through, until the edges are deeply golden, dark, and blistered, and the exterior is crunchy. The interior should remain vibrant violet and tender. Remove from the oven and let rest for 2 minutes.
   Look for Edges are dark, crispy, and blistered; a fork pierces the center easily.
   Tip For extra crispiness, use the convection setting if available.
5. 5Make the Miso Butter
   In a small bowl, combine the softened butter, white miso paste, honey, and grated garlic. Mash with a fork until the mixture is creamy, smooth, and well combined. Set aside at room temperature so it stays spreadable.
   Look for Butter mixture is smooth, creamy, and uniform in color.
   Tip Use softened butter for easier mixing. If the butter is too cold, microwave in 5-second bursts.

The potatoes should be deeply browned and blistered on the edges, with a crunchy exterior. The miso butter should be smooth and creamy, with a balanced sweet-savory aroma. The potatoes should be piping hot when the butter is added, so the heat melts it immediately.

Top and Serve

6. 6Top with Miso Butter
   Immediately after the potatoes come out of the oven, place a small dollop of the miso butter on each hot potato. The residual heat will melt the butter, allowing it to seep into every crack and crevice.
   Look for Butter melts and glistens over the crispy potatoes.
   Tip Work quickly while the potatoes are piping hot for maximum melting.
7. 7Garnish and Serve
   Sprinkle the potatoes with sesame seeds and thinly sliced scallions. Serve immediately while the potatoes are still crispy and the butter is melted.
   Look for Potatoes are garnished and ready to serve.
   Tip For extra crunch, add a little more sesame seeds right before serving.

The butter should be fully melted, glistening over the crispy potatoes. The sesame seeds and scallions add color and texture. The potatoes should be served immediately to maintain crispiness. The aroma is rich, savory, and slightly sweet.

Common mistakes

One common mistake is over-smashing the potatoes, causing them to break apart. Press gently but firmly to flatten to about 1/2-inch thick. Another is not drying the boiled potatoes well — excess moisture prevents crispiness.

Pat them dry with a kitchen towel before smashing. Also, avoid overcrowding the baking sheet; space the potatoes so air can circulate. Finally, don't skip flipping halfway through roasting; this ensures even browning on both sides.

How to tell it’s done

The potatoes are done when the edges are deeply golden, dark, and blistered, and the exterior is crunchy to the touch. A fork should pierce the center easily, and the interior should be vibrant violet and tender.

If the edges are not browning after 20 minutes, increase the oven temperature slightly or move the baking sheet to the top rack. The miso butter should be fully melted and glossy when served.