Melt the butter in a saucepan, over medium heat. Once the butter has melted, continue to keep it on medium heat to make brown butter, but stir frequently and keep an eye on it.
Check the colour of the butter solids frequently until the solids turn dark brown with a few black flecks (that's almost burnt butter).
At this stage, immediately add the sugar, corn syrup, salt and stir to combine. Add the cream soon afterwards, and reduce the heat to medium low. Let the sugar dissolve and the sauce come to a boil. Let it bubble (boil) gently for about 5 minutes, while stirring frequently.
Add the chocolate and vanilla and stir until the chocolate has completely melted.
Store in a glass bottle/jar with an air-tight lid. Let it cool slightly and pour over whatever you like.
Once the sauce cools, it does thicken. To make it pourable again, just microwave the jar (without the lid) for about 10-15 seconds, place the lid back on and give it a shake.
Recipe from The Flavor Bender by Dini Kodippili
Brown Butter Butterscotch Chocolate Fudge Sauce https://www.theflavorbender.com/brown-butter-butterscotch-chocolate-fudge-sauce/