Peel the Yukon Gold potatoes and cut them into approximately 2-inch (5 cm) chunks. Try to keep the pieces similar in size so they cook evenly. Avoid cutting them too small, since smaller pieces may become overly soft during parboiling.
Add the water to a large pot and bring it to a boil over high heat. Stir in the kosher salt and baking soda, then carefully add the potatoes. Return to a boil, reduce the heat to maintain a steady simmer, and cook for 10 minutes. The edges should begin to soften, while the centers should still offer slight resistance when pierced with a knife.
Drain the potatoes thoroughly in a colander: Leave them for 2 minutes so excess steam can escape. The surfaces should look relatively dry rather than glossy or wet. Removing moisture at this stage helps the potatoes roast instead of steam.
Transfer the drained potatoes to a large mixing bowl. Gently shake or toss them several times until the surfaces look slightly mashed and rough. You should see a thin, fluffy layer forming around the chunks. The pieces should remain mostly intact. If they begin breaking apart, stop tossing.
Preheat the oven to 425°F (220°C). Pour 1/4 cup (60 ml) of the olive oil onto the 18 × 13-inch (46 × 33 cm) rimmed baking sheet. Tilt the pan carefully to distribute the oil. Place the baking sheet in the oven for 5 minutes while the oven is fully heated. The oil should become hot and fluid without smoking.
Add the remaining 1 tablespoon plus 1 teaspoon (20 ml) olive oil to the potatoes. Sprinkle with the garlic powder, dried rosemary, and black pepper. Gently fold everything together until the seasonings are distributed across the rough surfaces. The potatoes should look lightly coated, not saturated with oil.
Carefully remove the hot baking sheet from the oven and place it on a heatproof surface. Add the seasoned potatoes, spreading them into a single layer with space between the pieces. You should hear some sizzling as the potatoes contact the hot oil. Position the flatter sides against the pan whenever possible to encourage a crisp, golden crust.
Return the baking sheet to the oven and roast at 425°F (220°C) for 45 minutes. After the first 25 minutes, use a spatula to turn the potatoes, gently releasing any pieces attached to the pan. Continue roasting for the remaining 20 minutes. The potatoes should develop deep golden-brown patches, crisp edges, and tender centers. If they brown unevenly, rotate the baking sheet when turning them.
Remove the potatoes from the oven and sprinkle with the fine sea salt. Add the chopped parsley, if using, and toss gently. Let the potatoes rest uncovered for 3 minutes before serving. Their crust should feel firm and crisp, while the inside should be soft and fluffy.