Preheat oven to 350 degrees. In a small saucepan, place 1 cup of sugar and 1/3 cup of water over medium-high- heat. Be attentive at all times until the sugar gets a golden color. Keep an eye on this at all times; you do not want to burn the sugar. As fast as possible pour the caramel into the ramekin and set aside.
In a mixing bowl, whisk the eggs, condensed and evaporated milk, vanilla and cinnamon (optinoal) until well combined.
Pour the mixture inside the ramekin with the caramel, place the ramekin inside a large baking pan. Pour hot water into the baking pan. Just enough to cover more than half of the ramekin for a baño de Maria.
Bake the flan 50 minutes to an hour. To make sure the flan is ready I like to insert a toothpick; if it comes out clean take the flan out of the oven and let it cool down for a few minutes
Then, place the flan in the fridge for at least an hour or until the next day if possible as it is best to eat this delicious dessert chilled.
You can also use small ramekins for individual flans. The trick to taking out the flan from the ramekin is to gently go clockwise with a table knife until you see the flan getting loose.