Preheat the oven to 425°F.
If using baby Dutch potatoes, cut them into quarters. If using yellow or russet potatoes, cut them into 3/4–1-inch pieces.
Thoroughly salt a medium pot of water over medium-high heat. Once at a boil, carefully add in the potatoes. Par cook them for 6-10 minutes (depending on size), or until they just reach fork-tender but don’t split when pierced.
Drain and toss the potatoes in the strainer several times, until they become coated in starch.
Carefully place the potatoes on a sheet pan and add the oil and a heavy pinch of salt. Toss to coat. Spread the potatoes out so they have plenty of space to crisp.
Roast for 35-40 minutes, flipping them every 15 minutes for even cooking. If they aren’t golden brown and crispy by the end of the 40 minutes, continue cooking, checking on them in 5-minute increments.
While the potatoes are cooking, place the feta, Greek yogurt, lemon juice, garlic clove, and olive oil in a food processor. Process on high for 20-30 seconds, then check the consistency. If it's still lumpy continue to process in 10-second increments.
Remove the potatoes and place them on a paper towel-lined pan or large plate to absorb any excess oil. Sprinkle with za’atar and toss to coat. Allow them to cool for 5 minutes.
To assemble place the whipped feta in a low bowl or plate and top with the slightly cooled potatoes. Garnish with harissa and a handful of cleaned herbs.