In a medium saucepan, stir granulated sugar, brown sugar, and cocoa powder together.
⅔ cup 133 grams, granulated sugar, ⅓ cup 73 grams, brown sugar, ½ cup 43 grams, cocoa powder
Add heavy cream and semi-sweet chocolate and heat over medium heat, stirring continuously until the chocolate has melted and the mixture just begins to bubble (but before it turns to a full boil). Reduce to low heat and simmer for 3 minutes, stirring frequently.
1 cup 237 ml, heavy cream, 4 ounces semi-sweet baking chocolate, broken into squares
Add butter and stir until the butter has melted. Remove from heat and stir in the vanilla extract.
½ cup 113 grams, salted butter, sliced into chunks, 1 tablespoon vanilla extract
Set aside to cool, then transfer to a mason jar or airtight container. Store in the refrigerator for up to 30 days.
To Serve: Portion the desired amount into a microwave-safe bowl. Heat in 15-second increments stirring after each time, until the sauce is warm.