bake
熇 centers on intense dry heat used for cooking: baking or roasting with fire.
熇 combines 火 (fire) with 高, which likely contributes the sound and suggests high heat or intensity. The exact historical development is uncertain.
Fire 火 beside 高 (tall/high) suggests a tall, intense flame used for baking. Picture a high fire in an oven baking bread.
For コク, imagine baking a cake in a very hot oven: the cake bakes until it's cooked, and 'cook' sounds like コク.