Preheat oven to 350°F (175°C).

1. In a medium saucepan over medium heat, melt the granulated sugar until it becomes a deep amber caramel, swirling occasionally. Do not stir.
2. Immediately pour the caramel into a round cake pan or flan mold, tilting to coat the bottom evenly. Set aside.
3. In a blender, combine sweetened condensed milk, coconut milk, evaporated milk, eggs, vanilla extract, and salt. Blend until smooth.
4. Stir in shredded coconut if using.
5. Pour the custard mixture into the caramel-coated pan.
6. Place the pan in a larger baking dish and carefully add hot water to the outer dish to create a water bath, filling halfway up the sides.
7. Bake for 50–60 minutes, or until the center is just set and a knife inserted comes out clean.
8. Cool to room temperature, then refrigerate for at least 4 hours or overnight.
9. To serve, run a knife around the edge of the pan and invert onto a serving plate.