Step 1

Whisk 1/2 cup olive oil and 1 tablespoon ground annatto together in a small saucepan. Cook over medium heat until simmering. Turn off the heat and let cool completely.

Step 2

Whisk 1/4 cup annatto oil, 2 tablespoons finely chopped lemongrass, 2 tablespoons peeled and finely grated ginger, 4 finely grated garlic cloves, 1/4 cup packed light brown sugar, 1/4 cup soy sauce, 1/4 cup cane vinegar, 2 tablespoons calamansi juice, 1 teaspoon kosher salt, and 1/2 teaspoon black pepper together in a large bowl.

Step 3

Add 3 pounds boneless, skinless chicken thighs and toss to thoroughly coat. Cover and refrigerate for at least 4 hours or up to overnight. (Alternatively, you can marinate the chicken in a gallon zip-top plastic bag, flipping the bag halfway through.) Store the remaining annatto oil in an airtight container at room temperature.

Step 4

Heat an outdoor grill to direct, medium-high heat (450°F to 500°F). Scrape the grill grates clean if needed.

Step 5

Remove the chicken from the marinade and let any excess drip off. Place on the grill smooth-side down in a single layer, with space in between each piece. Lightly brush the chicken with some of the reserved annatto oil, cover the grill, and cook until dark grill marks appear on the bottom, 4 to 6 minutes.

Step 6

Flip the chicken and lightly brush with annatto oil. Cover again and cook until grill marks appear on the second side and the thickest part of the chicken registers at least 165°F on an instant-read thermometer, 4 to 6 minutes more. Transfer to a serving plate. Serve with steamed white rice.