• Preheat oven to 325F. Keep a pot of boiling water ready.
• To make the caramel, mix sugar and 3 tablespoons of water in a saucepan at medium-high heat and stir only till it combines.
• Cook until caramel is amber (about 8 minutes), swirl the pan to colour evenly. Pour into cake pan.
• To make the custard, heat milk with ½ cup sugar over medium heat until it starts to steam and bubble around the edges (about 5-6 minutes). Do not let it boil.
• Whisk together eggs, yolks, remaining sugar and salt in a bowl. To this, add a ladle of the milk mixture and combine. Add a ladle of milk mixture two more times and combine after each addition. Whisk in the remaining mixture.
• Strain this mixture through a fine sieve and add the vanilla extract.
• Pour the custard into the cake pan. Place the cake pan in a roasting pan and set it into the oven. Add boiling water in the roasting pan, about half the side of the cake pan. Bake unti the custard is just set (about 50 minutes).
• Remove roasting pan from oven and carefully remove the cake pan from the water bath. Rest it on a wire rack for half an hour. Then, cover it with a plastic wrap and chill for atleast 8 hours or upto 3 days.
• To serve, use a sharp knife around the flan to unmold and place an upside down plate on the top. Invert and lift the pan.