In a blender, add the eggs, egg yolks, salt, sweetened condensed milk, evaporated milk and/or vanilla. Blend until very smooth, about 30 seconds. You don’t want to get it too frothy so try to avoid over blending. If you do over blend it, let it settle a bit so the bubbles can disappear. Set aside.
In a medium saucepan, set over medium-low heat, add the sugar and water. Cook on medium-low heat until the sugar has dissolved into the water completely. Then, turn the heat to high and allow to cook for about 5 full minutes, until the cooked sugar goes from clear to light golden brown. At this point, lower the heat slightly and keep cooking until it turns a golden brown.
Immediately pour it into the baking pan and twist it around until it’s in an even layer on the bottom.
Give the custard base a stir, just to make sure it’s still all combined. Pour it on top of the solid caramel. Cover with foil tightly. Transfer the flan to the water bath and fill up the water bath with water from a kettle.
Cook for 35 to 40 minutes, until slightly jiggly but still firm. Carefully remove it (it'll be hot!) from the oven and set aside.
Allow to cool on the counter for about 30 minutes and then transfer to the fridge to chill for at least 4 hours or overnight.
When ready to serve, run a knife around the edge and then invert onto a large plate. Smack the top of the pan to loosen the flan and then lift up the cake pan. Slice it up and serve.