Trim any large pieces of excess fat from the 700g chicken thighs, and if some thighs are much thicker than others, lightly flatten the thick parts with the base of a pan so they cook evenly. In a large bowl, whisk together the 80ml calamansi juice, 30ml vinegar, grated garlic, 20g ginger, minced lemongrass, 2 tbsp brown sugar, 2 tbsp fish sauce, 1 tsp fine salt and ½ tsp black pepper until the sugar dissolves. Add the chicken and turn it well until every surface is genuinely coated. Cover and refrigerate for at least 4 hours, or preferably overnight, but not much longer. The lemongrass should be minced so finely it looks almost like a paste, with no long fibres. That long, cold soak in a sour, aromatic marinade is what seasons the thighs all the way through rather than only on the surface.

During the final 15–20 minutes of marinating, take the chicken out of the fridge, still covered in its marinade, so it loses its chill before grilling. At the same time, rinse the 300g rice in several changes of cold water until the water runs mostly clear, then drain well. Put it in a medium saucepan with the 450–500ml water and the ½ tsp salt, if using, and bring to a boil over medium-high heat. Stir once, cover tightly, reduce the heat to low and cook for 12–15 minutes, until the water is absorbed. Take off the heat and rest, covered, for 10 minutes, then fluff with a fork. The grains should be genuinely dry and fluffy, never wet or sticky. That covered rest is what lets the trapped steam finish the rice evenly while the chicken grills.

Start preheating a grill, grill pan or heavy skillet over medium to medium-high heat, about 200–230°C at the grate. Put the 3 tbsp neutral oil and 1 tbsp annatto seeds in a small pan over low heat and warm gently for 2–3 minutes, swirling, until the oil turns a deep orange-red. It should never smoke or sizzle hard, and the seeds should not darken. Strain out the seeds, then stir in the 1 tbsp butter until melted, followed by the 1 tbsp calamansi juice, 1 tsp brown sugar and pinch of salt. If using annatto powder, stir it into the warm oil off the heat instead and skip the straining. The mixture should look glossy and lightly seasoned, never watery. That gentle, low-heat infusion is what draws out the colour without the bitterness of burnt annatto.

Lift each thigh out of the marinade and hold it over the bowl for a few seconds so the excess drips back. Pat very lightly with paper towel only where pools of liquid or clumps of garlic and lemongrass sit, leaving a thin, glossy coating on the chicken. Discard the used marinade, since it has been in contact with raw chicken and must never go into the basting oil. Lightly oil the hot grill grates or pan with neutral oil. The thighs should look evenly coated and damp, not dripping wet. That brief drain is what stops a sugary layer of marinade from burning on the grill before the chicken underneath has time to cook.

Lay the thighs on the grill, smooth side down, and cook for 5–7 minutes without moving them, until they release easily and show browned, lightly charred grill marks. Flip and cook the second side for 4–6 minutes, brushing the cooked side with the annatto oil several times now that the surface has set and coloured. Turn once more and baste the second side for the last 1–2 minutes. If flare-ups happen, move the thighs to a cooler part of the grill. The chicken is ready when it looks genuinely lacquered and glossy, the edges show caramelisation and char, the juices run clear, and the thickest part reads 74°C / 165°F. That late, repeated basting is what builds a glossy lacquer instead of a scorched, bitter crust.

Transfer the grilled thighs to a clean plate or board and rest them for 5–8 minutes, loosely covered if your kitchen is cool. Leave them whole for a classic presentation, or slice each thigh into 2–3 large pieces across the grain. Pour any juices collected on the plate into a small bowl to spoon over the bowls. The cut surfaces should look moist and opaque, with no pink at the centre. That short rest is what lets the juices settle back into the meat rather than running straight out into the rice.

Divide the fluffed rice among 4 bowls. Arrange the grilled chicken over the rice and spoon over any resting juices, then add a very light final brush of the remaining basting oil if you like more gloss. Scatter the 2 tbsp sliced scallions and the cilantro leaves over the chicken, and tuck the 4 halved calamansi and the lime wedges on the side of each bowl. Keep the bowl clean and simple, with the chicken as the focus over the white rice. Serve straight away while the chicken is hot. That bright citrus on the side is what lets everyone sharpen each bite at the table, the way inasal is traditionally eaten.