Warm the dairy. In a small saucepan, add the heavy cream, milk, and sugar. Heat over low to medium-low, stirring occasionally, until the mixture is steaming but not boiling. Aim for gentle heat to prevent scorching.

Add the white chocolate off-heat. Remove the pan from the burner. Add the chopped white chocolate and let it sit undisturbed for 1 minute to soften.

Whisk until smooth. Whisk slowly from the center out until the chocolate melts and the sauce is glossy and uniform. If small bits remain, return the pan to the lowest heat and whisk just until fully melted. Do not boil.

Finish the flavor. Stir in the vanilla and salt. Taste and adjust sweetness. If you like a thicker drizzle, let it cool for 5–10 minutes; it will thicken as it stands.

Use or store. Pour into a clean glass jar or squeeze bottle. Use immediately in coffee, or cool completely before refrigerating.