How to Make It
Preheat oven to 350°F. Place sugar in a medium skillet over medium-low. Cook, stirring constantly with a heat-proof spatula, until sugar begins to melt, adjusting heat to low if sugar begins to brown too quickly. Once sugar is completely liquefied and begins to turn a deep caramel color, about 12 minutes, carefully and quickly pour the syrup into a 9-inch metal pie pan. Using a potholder, turn pie pan to allow sugar to coat sides and bottom. (Be careful: The sugar syrup will be very hot, but will cool and set up quickly.) Set coated pie pan aside.
Combine sweetened condensed milk, whole milk, and eggs in a blender, and process until well blended, about 1 minute. Pour mixture into prepared pie pan. Place pie pan in a 13- x 9-inch baking dish, and, working from the side, carefully fill baking dish with water until water reaches halfway up side of pie pan. Cover pie pan loosely with aluminum foil. Bake in preheated oven until flan is set and a toothpick inserted in center of flan comes out clean, 1 hour to 1 hour and 5 minutes.
Remove pie pan from baking dish, and let flan cool in pie pan 1 hour. Cover flan loosely with foil, and refrigerate until completely chilled, about 6 hours or up to overnight.
To serve, run a paring knife around outside edge of flan to loosen. Place a serving plate over flan, and holding serving plate tightly to pie pan, invert. Carefully remove pie pan from flan, allowing syrup to coat top and pool around sides of the flan.