Make the sauce. Combine all of the ingredients in a medium mixing bowl and whisk well to combine. Cover bowl and store in the refrigerator for at least 2 hours. It will keep in the fridge for a couple of weeks.
Grill the chicken. Honestly, if you've grilled chicken in the past, you can use whatever method works for you and just pick up where I say, "Sauce the chicken." Here's what I did. I salted and peppered a dozen leg and thigh pieces, then started cooking them with the indirect grilling method I used for these Grilled Hoisin Chicken Thighs. Then I moved the chicken over the coals to brown and finish cooking uncovered, turning it occasionally and moving it away from flare-ups.
Sauce the chicken. When an instant read thermometer registered 165ºF, I began slathering the chicken liberally with the White Sauce, again turning it a couple/few times and saucing it each time. After 5 or so minutes, I declared this bridge open and transferred the chicken to a serving platter, let it rest for maybe 10 minutes, then served it.