Instructions:
- Prepare the Potatoes: Scrub potatoes well. Trim the ends flat. Slice potatoes lengthwise into thick 'slabs'—aiming for ¾-inch (2 cm) thickness.
- Par-Cook: Place potato slabs in a large pot, cover with cold, salted water. Bring to a boil and cook until just fork-tender (about 10-12 minutes). Drain immediately and let them steam dry on a rack for 5 minutes.
- Seasoning Mix: In a bowl, whisk together the 3 Tbsp olive oil, sea salt, pepper, thyme, smoked paprika, and minced garlic.
- Marinate/Coat: Gently toss the warm, slightly dried potato slabs in the seasoning mixture, ensuring all surfaces are coated. Let them rest for 15 minutes while you prepare the grill.
- Prepare the Aioli: Whisk the egg yolk, garlic paste, lemon juice, and Dijon mustard together. Slowly, drop by drop initially, whisk in the neutral oil until a thick emulsion forms. Slowly stream in the remaining 2 Tbsp olive oil. Season well.
- Preheat the Grill: Heat the grill to medium-high (around 400°F / 200°C). Clean and lightly oil the grates.
- Grill: Place the potato slabs directly onto the hot grates. Grill undisturbed for 5–7 minutes per side until deep golden brown grill marks appear and the edges are slightly crisp.
- Serve: Arrange the charred potato slabs on a platter and serve immediately alongside the zesty lemon aioli.