Combine soy sauce, sugar, and salt in small bowl; set aside. Heat oil in small saucepan over medium heat until it is just shimmering and registers 300°F on instant-read thermometer. Remove pan from heat and stir in pepper flakes, garlic, and soy sauce mixture. Let cool to room temperature, stirring occasionally, about 1 hour. Discard garlic before serving.

Makes about 1/2 cup