Mix the oil, melted butter, minced garlic, lemon juice, yellow curry paste, garam masala and turmeric in a small bowl.
Pour this mixture in an oven-safe baking dish and arrange the chicken leg and potatoes in it. Add the black peppercorns and bay leaf too.
Cover the dish with foil and pop it in an oven preheated at 425°F and bake for about 40 minutes.
Remove the foil and roast for another 5–10 minutes, until the chicken is golden, the potatoes are fork tender and the chicken reaches at least 165°F (74°C) in the thickest part without touching bone.
Notes
Use a bone-in, skin-on chicken leg for the juiciest results and beautifully golden skin.
Cut the potato into evenly sized cubes so the pieces cook uniformly and become tender alongside the chicken.
Use a small baking dish that fits the chicken and potatoes snugly in a single layer, allowing the potatoes to soak up the flavorful pan juices.
Adjust the yellow curry paste depending on your spice preference, or swap it with Vindaloo paste for a spicier version.
Cover the baking dish tightly with foil for the first 40 minutes to help the potatoes soften and keep the chicken moist.
Remove the foil for the final 5–10 minutes to allow the chicken skin to turn golden. The chicken should reach an internal temperature of at least 165°F (74°C).
Use a bone-in chicken thigh instead of a whole chicken leg if preferred, adjusting the cooking time as needed.
Remove the bay leaf and spoon the buttery, garlicky pan juices over the potatoes before serving.
Store leftovers in an airtight container in the refrigerator for up to 3–4 days. Reheat thoroughly before serving.