Melt the butter in a large heavy bottomed pot over medium/low heat. Preferably stainless steel – 2 quarts.
Stir the brown sugar as soon as the butter is melted, using a wooden spoon. Stir just until the sugar is combined with the butter.
Cook the mixture, without mixing, for 3 to 5 minutes. Or until the mixture is bubbly and caramel textured. You want it to be less grainy and more smooth.
Using a whisk, add the cream into the cooked sugar. Lower the heat to the low setting and cook until a candy thermometer reaches 225 degrees.
Remove from the heat and stir in the salt and vanilla.
Cool completely. Transfer to a glass jar and keep stored in the refrigerator until ready to use.
Notes
Try to avoid mixing the sugar mixture as it caramelizes.
Use a wooden spoon to begin and transfer to a whisk once you add the cream.
A good quality 2 quart pot is ideal for this sauce recipe.
Add a small amount of the salt and vanilla, taste, and add more as needed.