01 - Place the roasted hazelnuts in a food processor and blend until smooth and creamy, scraping down sides as needed, about 3 to 5 minutes.
02 - Gently melt the dark chocolate over a double boiler or in short bursts in the microwave until smooth. Allow it to cool slightly.
03 - Add the melted chocolate, cocoa powder, powdered sugar, whole milk, softened butter, vanilla extract, and sea salt to the hazelnut paste in the food processor.
04 - Process the mixture until completely smooth and creamy, pausing to scrape down the sides as necessary.
05 - Transfer the spread to a clean glass jar or airtight container. Let it cool to room temperature to thicken, then refrigerate for up to two weeks.
06 - Bring the spread to room temperature before serving to achieve the best texture.