Step 1

Adjust the oven rack to the center position and preheat oven to 450.

Step 2

Heat 2 quarts of water in a large pot and 2 tablespoons of kosher salt over high heat until boiling.

Step 3

Add in the baking soda, and gently drop in the potatoes and stir. The secret to adding something to boiling water or hot oil is counter intuitive. Reach your hand down close to the hot liquid and gently let go of the food. It will slide in rather than plop and save you from burns.

Step 4

Return to a boil, reduce to a simmer, and cook until a knife can slowly be inserted into a potato chunk without it being hard or falling apart, about 10 minutes after returning to a boil.

Step 5

Meanwhile, combine olive oil, with rosemary, garlic, and a few pinches of black pepper in a small saucepan and heat over medium heat. Cook, stirring the pan constantly, until garlic just begins to turn more yellow, about 3 minutes.

Step 6

Quickly strain oil through a fine-mesh strainer set in a large bowl and set aside the garlic/rosemary mixture, reserving it separately.

Step 7

When the potatoes are ready, drain the water off carefully into the sink and let the potatoes rest in the hot pot for about 30 seconds to so that any excess moisture can evaporate.

Step 8

Transfer to the bowl with infused oil, season to taste with a little more salt and pepper, and then shake and toss the potatoes around vigorously until a thick layer of mashed potato–like paste has built up on the chunks. Transfer the sweet potatoes to a large rimmed baking sheet and separate them so they aren't touching.

Step 9

Transfer the pan to the oven and roast for 20 minutes. Using a thin, flexible metal spatula like this one to release any stuck potatoes, shake the pan and turn the sweet potatoes.

Step 10

Continue roasting until a golden deep brown color appears and they are crisp all over, turning and shaking them a few times during cooking, 25 to 35 minutes longer.

Step 11

Transfer the sweet potatoes to a large bowl and add the garlic/rosemary (or thyme) mixture and minced parsley. Toss to coat and season with more salt and pepper to taste.

Step 12

Serve immediately.