In a medium pot, whisk together the brown sugar, granulated sugar, cocoa powder, and salt. Then whisk in your cream

Place over medium heat and cook, whisking frequently, until the mixture comes to a gentle simmer and the sugar is fully dissolved. The sauce will start to thin and get dark and shiny before it simmers

Let it simmer for about 3 minutes, stirring occasionally

Remove the pan from the heat and immediately stir in the butter. Once the butter has been completely stirred in, add in your chopped chocolate, stirring until smooth and fully melted

Add the vanilla extract and mix until combined

Transfer to a jar and allow the sauce to cool for about 5–10 minutes before serving. As it cools, it will thicken to the perfect fudgy consistency

To reheat, either add to a pot and stir until loosened or microwave for 5-10 second intervals, stirring until you’ve reached your desired consistency