• Preheat oven to 325 degrees Fahrenheit. Place 4 (6-ounce) oven-safe ramekins in a 9 by 16 inch baking dish. Bring about 4 cups of water to a boil and then leave on a simmer. You will need this later on for the water bath.
• Take out/measure out your heavy cream, milk, vanilla extract, salt and egg yolks. Whisk the egg yolks in a medium sized heat proof bowl next to the stovetop. Place a large sieve over a heat proof bowl. 
• In a medium sized heavy bottomed sauce pot, cook the butter and brown sugar over medium heat using a wooden spoon to stir while it cooks. Do not step away from the pot as you'll need to keep stirring and also watch for cues to know when to add the cream. Cook for about 8 minutes.
• At about 8 minutes, you should notice the mixture start to brown and develop a consistency similar to wet sand. The mixture may also start to smoke a little which is normal. As soon as the mixture starts to smoke, slowly pour in one cup of the cream. The mixture will sputter and seize up but keep stirring. Stir in the rest of the cream and milk.  Cook and stir until the seized sugar dissolves. Use your wooden spoon to break up and stir while the sugar melts. If the mixture begins to boil, lower the heat.  Once the mixture is mostly smooth, add salt and vanilla extract. Mix well. Remove from heat. 
• Pour a little of the hot butterscotch mixture to the yolks as you whisk them. Add just enough of the cream mixture til the egg yolks are warm to the touch. 
• Pour the egg yolk mixture into the butterscotch mixture. Whisk gently just to combine. Pour the mixture through a large sieve then divide it evenly between 4 six-ounce ramekins.
• Carefully fill the baking dish with hot water halfway up the ramekins. Take care not to get any water in the custards. Tent the baking dish loosely with aluminum foil and bake 30-40 minutes. To check for doneness, gently tap or shake each ramekin (with an oven mitt on your hand!) If it ripples like water, cook another five minutes then check again. They are done when they jiggle like Jello. Remove from oven.
• Allow ramekins to cool in the pan (with the water still in it) on the counter for one hour then cover and cool in the refrigerator for at least 2 hours. Store, covered in the refrigerator for up to 3 days. Top with whipped cream** (recipe below). Decorate with a sprinkle of brown sugar and flaky sea salt, if desired. 

Whipped Cream

• In the bowl of an electric mixer fitted with the whisk attachment, beat the heavy cream, vanilla, and powdered sugar on medium high speed for 2-3 minutes until medium peaks form. Use right away or cover and chill in the refrigerator for up to 24 hours.