Finely dice onion and mince garlic & ginger. (I like to peel ginger with a spoon or vegetable peeler first.) Cut potatoes into 1/2-inch pieces so they cook evenly.
Heat 2 tablespoons coconut oil in a large, deep pan over medium-high heat. Add onion and sauté for 3–5 minutes, until golden. Add garlic & ginger and stir for 30 seconds. Reduce heat and add 1-1/2 teaspoons curry powder, curry paste, and coriander. Stir frequently for 2–3 minutes, until fragrant. Add potatoes and stir for 1 minute to coat in the spices.
Pour in coconut milk & chicken stock, scraping up any browned bits from the bottom of the pan. Press potatoes into the liquid and bring to a steady simmer over medium heat (bubbling around the edges, but not rapidly boiling). Cook uncovered for 20–30 minutes, stirring occasionally, until potatoes are fork-tender and sauce has thickened. Mine usually takes 20–25 minutes. If sauce reduces before potatoes are tender, lower heat slightly and add a splash of chicken stock. If potatoes are cooking slowly and sauce isn't reducing, increase heat slightly.
Meanwhile, cut chicken into 1-inch pieces and toss with cornstarch, remaining 1/2 teaspoon curry powder, 1/2 teaspoon salt & 1/4 teaspoon pepper. Heat remaining 1 tablespoon coconut oil in a separate pan over medium-high heat. Add chicken and cook for 4–7 minutes, stirring only occasionally to allow some browning, until nearly cooked through. Avoid overcooking, since chicken will finish cooking in the curry. Add chicken to the curry and simmer for 1–2 minutes, or until fully cooked (165°F). Stir in sugar, cilantro, & lime juice adjusting amounts to taste. Add soy sauce if desired, starting with 2 teaspoons and adjusting to taste.
Remove curry from heat. Taste and adjust seasonings, adding more salt & pepper if needed. Serve over warm rice with naan on the side. Both help balance the heat from the curry!
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Notes
Note 1: Yellow curry paste can be tricky to find in grocery stores, so I usually order mine on Amazon. I love Maesri yellow curry paste, but Mae Ploy Yellow Curry Paste is another great option. Flavor & heat vary quite a bit by brand. Start with 1 tablespoon for a milder curry (full-fat coconut milk helps balance the heat) or use up to 4 tablespoons for a much spicier version. Start small since you can always add more!Note 2: To cook basmati rice: Fill a large pot with water and bring to a boil. Once boiling, generously salt the water and add the rice. Boil for about 10 minutes, then taste the rice to make sure it is tender. Drain well and return the rice to the dry pot. Cover and let steam until ready to serve.Note 3: To warm naan, heat a dry skillet over medium-high heat. Add naan and cook for 30–60 seconds per side, until warm and lightly charred. Wrap in a towel to keep warm. Alternatively, warm naan in a toaster or microwave covered with a damp towel.Storage: To freeze leftover curry paste, drop small spoonfuls onto a parchment-lined tray and freeze until solid. Transfer to a freezer-safe container and freeze for up to 3 months. Thaw individual portions overnight in the fridge as needed.Leftovers: Store curry in an airtight container in the fridge for 3–4 days. Reheat gently on the stovetop, adding a splash of chicken stock if needed. Store rice separately.