Begin by creating a marinade for the boneless chicken thighs. In a mortar and pestle, combine garlic cloves, coriander roots, and white peppercorns, and mash into a fine paste. Mix this paste with fish sauce and coat the chicken thoroughly. Let it marinate for at least 10 minutes, or ideally for several hours in the refrigerator.

While the chicken marinates, prepare the slaw dressing. Crush garlic cloves and birds’ eye chillies together in a mortar and pestle until smooth. Mix this paste with roasted peanuts, sugar, fish sauce, and fresh lime juice in a bowl. Set aside to allow the flavors to meld.

Heat a grill or non-stick frying pan over medium-high heat and add vegetable oil. Once shimmering, place marinated chicken thighs skin-side down on the grill. Sear for 2 minutes, flip, and cook for another 2 minutes. Lower the heat and grill for an additional 6-8 minutes until the internal temperature reaches 165°F (75°C).

After grilling, toast the burger buns by lightly buttering the insides and grilling them for 2-3 minutes until golden brown and slightly crispy.

Toss the finely sliced cabbage with the prepared slaw dressing, then spread mayonnaise on the toasted buns. Layer with butter lettuce, tomatoes, and the grilled chicken. Top with cabbage slaw and place the other half of the bun to complete the sandwich.

Serve your spicy Thai fried chicken sandwich fresh on a decorative plate, optionally garnishing with fresh coriander.