01 - Melt the chopped chocolate and butter in a heatproof bowl set over simmering water, stirring until smooth and combined.
02 - Remove from heat and whisk in whole milk until the mixture becomes glossy and smooth.
03 - Stir in powdered sugar, vanilla extract, and a pinch of sea salt. Mix in hazelnut or peanut butter if desired.
04 - Allow the spread to cool slightly, then transfer to a clean airtight jar. It will thicken upon cooling.
05 - Refrigerate for up to two weeks. Bring to room temperature before use for optimal texture.