01 -
Place a large, empty roasting pan in the oven and preheat the oven to 450°F.
02 -
Rinse the potatoes under cold water to remove excess starch and add them to a large stock pot. Cover the potatoes with cold water, add 2 tablespoons kosher salt and baking soda, and set over high heat.
03 -
Bring the water to a boil and cook the potatoes until they are just barely fork-tender and the edges start to flake, approximately 25 minutes. Drain the potatoes and let them dry fully in the colander.
04 -
Remove the preheated roasting pan from the oven, add the duck fat, and heat until melted. Shake the potatoes in the colander to rough up the edges, then carefully add them to the roasting pan. Season with salt and pepper and toss gently to coat. Nestle in the garlic head, cut-side down, and return the pan to the oven.
05 -
Cook the potatoes, tossing every 20 minutes, until they are deeply golden brown and crispy all over, approximately 55 to 60 minutes total.
06 -
Remove the garlic and push out the individual roasted cloves. In a bowl, mash the garlic cloves with the chopped rosemary and olive oil using a fork. Add this mixture to the roasting pan and toss with the potatoes to coat.
07 -
Return the roasting pan to the oven and cook for an additional 5 minutes, or until the rosemary is fragrant and the garlic is lightly toasted. Adjust seasoning with flakey sea salt as desired. Transfer the potatoes to a serving bowl and serve immediately.