Prepare Caramel - Caramelized Sugar:
In a heavy-bottom, high-sided saucepan over low to medium-low heat, combine 1 cup sugar and a drop of lemon juice (the lemon juice keeps the mixture from hardening or crystalling). NOTE: I find that maintaining a low heat, I have more control over the caramelizing process, as it is really easy to burn.
Cook, stirring constantly, with a wooden spoon or silicone spatula until sugar dissolves and mixture just begins to simmer. Sugar melts at about 320 degrees F. and will turn to a clear liquid at that temperature. Continue stirring and cooking, approximately 8 to 10 minutes, or until you get a nice golden brown caramel. Make sure not to overcook as the caramel can burn. NOTE: Boiling times will vary according to different stove tops and other factors.
Pour the caramel into the loaf pan, making sure that the caramel completely covers the bottom surface of the pan. Set aside and let the caramel cool while making the flan mixture.
Preheat oven to 350 degrees F. or 180 degrees C. Adjust oven rack to center position.
In a blender, combine evaporated milk, condensed milk, orange zest, whole or 2% milk, eggs, vanilla extract, and salt; process until smooth. Let the flan mixture sit approximately 10 to 15 minutes.
After resting, remove any top foam that formed when blending the ingredients and discard. Stir the flan mixture just before pouring in your loaf baking pan.
Pour the prepared flan mixture into the loaf pan. Place the filled loaf pan into an ovenproof roasting or baking pan. If cooking custards in a metal pan, cover the bottom of the pan with a layer of newspaper to ensure an even temperature on the bottom.
Bring the water for the water bath to a light simmer on top of the stove; carefully pour hot water into the baking pan to come half-way up the sides of the loaf pan. For ease of carrying, first place the larger pan (containing the filled loaf pan) on the oven rack, then pour the boiling water into the large baking pan. It is so much easier than moving the pans with water in them.
Bake 60 to 70 minutes (depending on depth of your pan) or until set around the edges but still loose in the center. When the center of custard is just set, it will jiggle a little when shaken, that's when you can remove it from the oven (the flans will continue to set as they cool). If using a digital instant-read thermometer, inserted in the centers, it should register 180 degrees F. Begin checking temperature about 10 minutes before recommended times.
Remove from oven and remove the flan pan from the water bath. Place on your counter and let cool approximately 60 minutes.
Refrigerate at least 4 hours or overnight.
To Unmold and Serve:
When ready to serve, remove from refrigerator at least 1 hour before unmolding.
Using a thin knife, separate the edge of the flan from the pan to make sure that the flan edges are not sticking to the sides of the pan.
Choose a rimmed serving dish that has a flat bottom just slightly wider in diameter than the inside diameter of the cake pan. Place your serving dish upside down on top of the flan pan, and holding both together tightly, flip quickly so the serving dish is right side up and the flan pan is upside down. Do not remove the flan pan immediately. Let it sit for at least 15 minutes while the caramel drips from the pan all over the top and sides of the flan.
Makes 6 servings (depending on size of your servings).
Tres Leches Mexican Flan Recipe: https://whatscookingamerica.net/desserts/mexicanflan.htm