Fire radical on the left - pictograph of flames. Indexes 熘 in the cooking-with-heat family with 炒 stir-fry, 炸 deep-fry, 烤 roast. Marks the character firmly as a method of applying heat to food.
Right side 留 supplies the sound with a tone shift: liú → liū. 留 alone means "to stay, to retain" - a faint semantic hint at how 熘 works: a starchy glaze stays on the food, clinging to each piece. Same phonetic in 溜 slip and 馏 distill.
