Bloom gelatin by mixing powder with icy-cold water and letting it hydrate for 10 minutes, or soak gelatin sheets in cold water for the same time.
Heat water, sugar, and corn syrup in a saucepan over medium heat, stirring occasionally, until it reaches 217°F (103°C) or starts bubbling hard.
Remove from heat and stir in sweetened condensed milk until well combined.
Add the bloomed gelatin and mix until fully dissolved.
Pour the hot mixture over white chocolate in a large bowl, stir, then emulsify with a hand blender, keeping the blender slightly tilted to minimize air bubbles.
Optionally, add food coloring.
Allow the glaze to cool to 86-95°F (30-35°C).
The ideal temperature depends on the environment, but around 91°F (33°C) works well.
Place the frozen cake on a wire rack over a baking sheet.
Remove from the mold and ensure it is solidly frozen.
Pour the glaze generously over the cake in a circular motion, covering the sides evenly.
Use an offset spatula to smooth the surface and remove excess glaze.
Trimming any excess glaze from the bottom for a clean finish.
Once dripping stops, transfer the cake carefully onto a serving plate or cake board.