Combine half of the heavy cream, allulose, chocolate, and salt in a medium saucepan. Place the saucepan over low heat and cook, whisking constantly, until the chocolate has melted. Whisk in the remaining heavy cream and remove the pan from the heat. Stir in the vanilla.

Pour the chocolate sauce into a 2-cup mason jar or another container with a lid. Refrigerate until serving time.

To serve, heat it gently in the microwave until just warm.

Drizzle the sauce over ice cream, pudding, or cake, or use it to make chocolate milk, milk shakes, or chocolate ice cream soda.