Put 1/2 cup of the sugar in a small saucepan over medium heat and cook until it begins to melt and turns brown around the edges. Pull the melted sugar around the edges toward the center of the un-melted sugar with a heatproof rubber spatula. Continue cooking, pulling the melted sugar, until all the sugar is melted and the caramel is uniformly dark amber (it should smell caramelly but not burnt), 10 to 12 minutes total. (If you still have undissolved lumps of sugar, stir it off heat until melted.) Pour the caramel into 8-by-2-inch deep cake pan in an even layer, 1/8 to 1/4 inch deep. Let the caramel cool; it will crack as it cools and that's ok.
Bring the cream, milk and vanilla bean to a simmer in a medium saucepan over medium-high heat. Remove from the heat and steep for 30 minutes.
Arrange a rack in the middle of the oven and preheat to 350 degrees F. Bring a large pot of water to a boil.
Put the eggs, salt and the remaining 1/2 cup sugar in a blender and puree on low speed until smooth and the sugar is dissolved, about 1 minute.
Strain the cream mixture into the egg mixture and blend at low speed to combine, discarding any solids. Skim the foam off the top and transfer to the prepared baking dish. Remove any remaining foam from the top and cover the dish tightly with foil.
Line a roasting pan with a clean kitchen towel; this will keep the baking dish from sliding and it will insulate the flan, preventing it from overcooking. Set the baking dish on a towel and pour boiling water into the roasting pan until it comes halfway up the sides of the baking dish; the flan should not be floating. Bake the flan until it looks set like gelatin(it will wobble when gently shaken), 35 to 45 minutes. Transfer to a wire rack, remove the foil and let cool. Cover the dish with plastic and refrigerate until set and cold, at least 3 hours and up to 24.
When ready to serve, run a paring knife around the edges of the flan to loosen. Invert it onto a platter. Serve cold. The flan can be made 1 day ahead. Cover and chill. Unmold and serve.