Add the sugar to a medium saucepan in an even layer, and warm over medium heat until the sugar at the edges of the pan begins to melt. Meanwhile, warm the cream slightly in the microwave or a small saucepan, and set aside.

Continue cooking, using a spatula to stir the melted sugar from the bottom and edges into the center, until all of the sugar is dissolved and the mixture turns to a rich amber or caramel color. When it reaches this color, remove the pan immediately from the heat.

Very slowly pour the warmed cream into the caramel, whisking rapidly as you pour, followed by the butter. Whisk in the salt and 1 cup of the milk. (If the mixture seizes up during this process, return the pan to low heat and stir gently, breaking up any lumps as well as you can. A few remaining lumps are OK.)

Place the egg yolks in a medium bowl and whisk to blend. Now slowly pour most of the caramel-cream mixture into the bowl with the eggs, whisking constantly to incorporate and prevent the eggs from curdling. (This process is called tempering, and is what makes your batter into delicious, creamy custard!)

Return the custard to the saucepan and cook over medium heat, stirring constantly, until the mixture thickens slightly and coats the back of a spoon. (If you have an instant-read or candy thermometer, the temperature to aim for here is approximately 170 degrees F, or 77 degrees C.)

Set a fine mesh strainer over a medium bowl, and pour the custard through to strain out any small lumps. Stir in remaining 1 cup of milk and the vanilla extract. Let mixture cool slightly, stir well, then cover and refrigerate until well-chilled, at least 8 hours, preferably overnight.

Freeze in an ice cream maker according to the manufacturer’s instructions. Once your ice cream is churned, quickly stir in pretzels or any other mix-in as desired, then pour into a loaf pan or other container and chill in the freezer until firm.