Preheat oven to 425°F. Drizzle oil on sheet pan and preheat in oven until the oil is shimmering.

Add potatoes and baking soda to a medium pot and cover with 3 inches cold water. Salt heavily and bring to a boil. Cook until potatoes are knife tender, about 15 minutes. Drain the potatoes and let cool for 5 minutes.

Carefully spread the potatoes on the preheated baking sheet with oil. Bake until golden brown, about 30 minutes, flipping as needed to brown all sides (check every 10 minutes).

Meanwhile, mix the cheese, garlic, herbs, and black pepper in a large bowl.

In a small bowl, mix the mayo, harissa (start with a little and add more if desired), and lemon juice. Season with salt and pepper.

Once the potatoes are golden brown, transfer them to the cheese mixture and toss to combine. Spread the harissa mayo on a plate, top with potatoes and serve immediately.