Yield: 4 servings
In a small bowl, whisk together soy sauce, water, sugar, fish sauce, and garlic until sugar is dissolved, about 30 seconds. Set aside.
Pour oil into a 3-quart saucier or saucepan. Add potatoes, arranging them cut-side down in a single layer. Set saucier over medium-high heat and cook, uncovered, until potatoes are light golden-brown on cut-side, 5 to 6 minutes.
Lower heat to medium-low, add soy sauce mixture and stir to combine with potatoes. Cover saucier with a lid, and cook until potatoes are completely tender and offer no resistance when pierced with a cake tester or paring knife, about 10 minutes.
Remove lid and increase heat to high. Cook, uncovered, stirring constantly with a heat-resistant rubber spatula, until liquid has reduced and thickened to a sticky caramel consistency that fully glazes the potatoes, 1 to 2 minutes.
Remove from heat, and transfer potatoes to serving bowl. Drizzle with sesame oil, sprinkle with sesame seeds, and serve.