Combine 1 cup sugar with ¼ water in a small deep, heavy saucepan. Bring to a boil over medium-high heat, stirring just until the sugar melts. Continue to cook, tilting the pan from side to side occasionally, until the sugar is the color of an old penny.
Carefully pour the caramelized sugar into a 10 – 12 cup Bundt pan, swirling to coat the pan with caramel.
Heat the milk with the salt over medium heat just until warm.
Whisk the eggs and the remaining 1 cup sugar in a large bowl and add about ½ cup of the warm milk while whisking. Add the rest of the milk and the vanilla and mix well. Pour into the pan over the caramel. Cover with foil.
Place the pan into a large roasting pan, place in the oven, and pour hot water into the roasting pan, coming about halfway up the sides of the Bundt pan.
Bake for 1 hour. Check to make sure the flan is cooked through. Remove from the oven and cool to room temperature. Refrigerate for at least 4 hours.
Run a knife around the edges of the pan. Place a plate or platter with a little bit of a lip (to catch the caramel) on top of the pan and invert.