Instructions
Step 1
Make the sauce: To a food processor, add the blueberries and 2 tablespoons of the vinegar. Pulse to break up the berries and get some juices flowing.
Step 2
Transfer the pulverized berries to a medium pot and add the sugar, chile flakes, bay leaf, cinnamon stick, and remaining vinegar. Bring to a simmer over medium heat, then turn the heat to low, cover the pot, and cook, stirring occasionally, for 1 hour.
Step 3
Carefully transfer the hot sauce to a blender. Remove the knob from the top of the blender lid and cover with a dish towel to prevent an explosion. Blend the sauce until it’s as smooth as possible, then strain through a fine mesh sieve directly back into the pot. Bring to a simmer over medium-low heat and cook, stirring occasionally, until the sauce has reduced by about one-third of its original volume, 25–30 minutes. It should coat the back of a spoon and have the viscosity of maple syrup. Set the sauce aside to rest for 8–24 hours. It will keep for months, covered, in the refrigerator.
Step 4
Make the chicken: Heat a gas or charcoal grill to to 350°F. Bring the chicken to room temperature 30 minutes before you plan to grill, then season with salt and black pepper.
Step 5
Place the chicken, skin side up, on the grill and close the lid. Cook, covered, for 20 minutes. Baste with the blueberry sauce every 5 minutes for an additional 20 minutes, keeping the lid closed between basting. Using tongs, flip the chicken and continue cooking, basting with the blueberry sauce every 5 minutes and keeping the lid closed between basting, until the skin is caramelized and a thermometer inserted into the thickest part of a thigh reads 165°F, about 10 minutes more.
Step 6
Remove the chicken from the grill, toss in ½ cup of the blueberry sauce, and set aside to rest for 10 minutes. Carve the chicken into six or eight pieces and toss once more in another ½ cup of the blueberry sauce. Serve the chicken warm or at room temperature.