Place the milk, 1 cup cream, and sugar in a medium saucepan and bring just to a boil over medium heat, stirring occasionally.
1 cup whole milk, 1 + ¼ cup heavy cream, ¼ cup sugar
Whisk the eggs in a medium bowl just until frothy.
3 large eggs
Slowly add half the hot milk mixture to the eggs, whisking constantly as you pour the milk mixture in; then pour this mixture back into the saucepan.
Place the saucepan back over medium-low heat, and cook the custard, stirring constantly, until it thickens enough to coat the back of a spoon; keep a close eye on it, as it should never come to a boil. When thick enough, the custard should register 170°F on a candy thermometer. Pour the custard through a fine-mesh strainer into a large bowl, and set it aside.
Wash and dry the saucepan, and add the caramel, remaining ¼ cup cream, salt, and vanilla. Cook and stir the mixture over medium-low heat, until completely smooth, stirring often. Thoroughly stir the warm caramel into the warm custard, leaving no streaks. Cover the surface of the custard mixture with a piece of plastic wrap and refrigerate until chilled, at least 4 or up to overnight.
1 + ¼ cup heavy cream, 10 to 11 ounces salted caramel sauce, ¼ teaspoon fleur de sel, ½ teaspoon vanilla extract
Taste the cream mixture for salt, adding more if desired. Freeze the custard in an ice cream maker according to the manufacturer’s instructions.
Transfer the finished ice cream to an airtight container and place it in the freezer until ready to serve. To serve: top with a sprinkle of pretzel salt and a drizzle of caramel, if desired.