Preheat the oven to 450°F. Find a baking sheet large enough to accommodate a 9-inch pie dish or cake round with a flat top. It must lay flat for the flan to come out of it and onto a serving dish without breaking.
Set a light-colored sauce pot over medium heat and add the sugar and 1/4 cup of orange juice. (If the orange didn’t release a ¼ cup of juice, make up the difference with water.) Heat the sugar and melt it until it turns light golden brown, then take the pot off the heat. The sugar will continue to brown off the heat. Do not stir the sugar, which can cause it to recrystallize and get grainy. Instead, swirl the pan.
Pour the hot sugar syrup into the 9-inch pie dish or cake round, coating the bottom in an even layer. Set aside.
Add the sweetened condensed milk, evaporated milk, heavy cream, bay leaf, strips of orange zest, and a pinch of salt to a medium pot. Heat until steaming, then take off the heat, cover, and steep for 20 minutes.
When the milk mixture has finished steeping, beat 4 eggs with 1 tablespoon of vanilla in a large bowl. Pour the steeped milk mixture through a fine mesh sieve into the egg mixture and mix. Do not whip; you don't want to incorporate air into the liquid.
Meanwhile, bring 2 quarts of water to a boil for the water bath. Pour the milk and egg mixture into the prepared 9-inch pie dish or cake round, then place the pie dish or cake round onto the baking pan. Place the baking pan in the oven and fill halfway with boiling water to surround the pie dish or cake round, creating a water bath.
Lower the temperature of the oven to 350°F. Bake the flan for 60 to 70 minutes until the custard has set but still jiggles like thick lava in the middle. Let the flan cool completely. Then, place it in the fridge to set for at least 8 hours.
To serve the flan, run a knife around the edges of the pan. Then, top the 9-inch pie dish or cake round with the serving plate and carefully flip it over. Tap the baking dish gently to help the flan release. When you hear the flan release from the pie dish, remove the pie dish carefully and let caramel sauce flow over the flan.