Put 1/2 cup cream, brown sugar, salt, and butter into a saucepan. Bring to a boil over medium high heat, stirring constantly until sugar dissolves. Lower heat to a simmer and continue cooking, stirring occasionally, until the mixture is deep brown in color, about 8-10 minutes. Remove from heat, transfer to a large glass measuring cup and let cool.
Once mixture has cooled, whisk in the egg yolks, remaining 1/2 cup cream and milk. Carefully pour mixture into ramekins and place ramekins in a deep sided baking pan. Set pan on oven rack and slowly pour water into pan, until water is a little more than half way up the sides of the ramekins.
Bake for 22-25 minutes, checking near the end of baking time. The mixture is done when it’s set around the sides but still jiggles a little in the middle. Remove pan from oven and carefully transfer ramekins to a place to cool, using tongs or a spatula.
Once dishes have cooled, sprinkle with sugar and optional butterscotch chips. Carefully brown brulee tops with a kitchen torch or under the broiler, watching carefully. Sprinkle with salt and serve.
Refrigerate up to 5 days if desired.