Make the butterscotch: melt the butter in a heavy-bottomed saucepan. Add the dark brown sugar and the salt can cook until the mixture comes to a boil. Stirring constantly, cook until the mixture breaks apart and then comes together again and just begins to smoke.

Immediately pour in the heavy cream. It will bubble and spit, so be careful, and the mixture may harden up. Just keep stirring over medium-low heat until all the butterscotch melts back into the cream.

Whisking constantly, temper the butterscotch mixture into the egg yolks.

Off the heat, stir in the vanilla extract.

(Optional Step)For creamiest results, refrigerate the custard overnight.

Preheat oven to 275F. Place a tea towel in the bottom of a half-sheet pan, folding the edges in so they don't hang over the rim of the pan. Bring a quart of water to a boil.

Strain custard through a fine mesh strainer into a spouted measuring cup.

Divide the custard evenly among four 5oz ramekins. Pass the flame of your kitchen torch over the surface of the custard to pop any bubbles.

Place the filled ramekins on the tray and put the tray in the oven.

Carefully pour the boiling water into the pan so it comes halfway up the sides of the ramekins. Take care not to splash any water into the custard.

Bake until custards are set around the edges and still a little jiggly in the centers, about 35-40 minutes, depending on your oven.

Remove the ramekins to a cooling rack. I use silicone tongs to grab them by the handles, leaving the water bath in the oven to clean up after it has cooled off.

Once the custards have cooled, chill for at least 2 hours. Cover once they have reached refrigerator temperature.

When ready to serve, remove the custards from the fridge. If there is any condensation on the surfaces, use the corner of a paper towel to wick it away.

Pour a generous spoonful of either dark brown or granulated sugar onto each custard. If using granulated sugar, tilt the ramekins to completely cover the tops of the custard. Pour off any excess sugar. If using dark brown sugar, use your fingers or an offset spatula to carefully spread a thin, even layer of sugar over each custard.

Use your kitchen torch to first melt and then evenly (as evenly as possible, anyway) caramelize the sugar.

Allow to cool off for maybe 1 1/2 minutes before serving. This allows the caramel to harden into a lovely sheet of edible glass. Use the side of your spoon to crack through and enjoy.