01 -
Get 2 quarts of water boiling in a large pot. Heat your oven to 450°F and put a rack at the bottom.
02 -
Peel all potatoes. Cut Yukons into 1½-inch pieces (max 2 inches). Slice the Russet lengthwise into quarters, then crosswise as thin as possible.
03 -
Add 2 tablespoons kosher salt to boiling water along with potatoes. Simmer about 8 minutes until Yukons are just tender and Russets are very soft.
04 -
Drain potatoes and return to hot pan briefly. Transfer to a bowl and vigorously toss for 1 minute until starchy coating forms. Mash any Russet pieces.
05 -
Toss with olive oil, salt, and pepper until coating thickens. Transfer potatoes individually to preheated roasting pan. Roast 40 minutes, flipping every 20 minutes.
06 -
For plain potatoes, roast 7 more minutes. If using rosemary, make a paste with olive oil, spread over potatoes, then roast final 7 minutes until deeply golden and crispy.