[Caramel Sauce]
Add granulated sugar and 1.5 Tbsp water in a small pot and heat over medium heat. Please don't stir it to prevent the sugar from turning into crystals.
When the edge becomes yellow, move the pot sometimes to make it evenly golden.

When it turns golden brown and the steam rises strongly, immediately turn off the heat.
Add 1 Tbsp water. Please be careful as the hot splash. Move the pot to smooth it.
Add rum, and move the pot to mix. Pour the caramel sauce into a loaf pan. Move the pan to spread. Set aside.

[Custard]
☆ Preparation
・Prepare plenty of boiling water.
・Preheat an oven to 170℃ / 338 F.
Put milk, condensed milk, and granulated sugar in a small pot. With stirring, heat it over medium heat until 40-45°C / 104-113 F.
Break eggs into a large bowl. Use a whisk to beat gently so as not to foam until smooth.

With stirring, pour the warm milk little by little into the egg. After adding all, continue to stir for 30 seconds. Add vanilla bean paste and stir well.

Pour it over the hardened caramel sauce while straining with a tea strainer. Gently put a sheet of paper towel on the surface and remove the scum.

Line the deep-sided container with 2 sheets of paper towel. Pour plenty of 50℃ / 122 F hot water. (If you mix water and boiling water in the same ratio, it reaches about 50℃ / 122 F.)
Place the pan in hot water. Make sure that the top of the water reaches half the height of the pan.

Bake it at 170℃ / 338 F for 5 minutes, and at 150℃ / 302 F for 25 minutes until the center shakes a little.
Remove from hot water, and quickly cool down with cold water (ice water or water with ice packs). Cool down completely, and let it cool in a fridge overnight.

[Remove from the pan]
Put the bottom of the pan in hot water for 1 minute to loosen the caramel a little. Slide a knife around the edges.

Cover it with a large plate on the top, and shake lightly. After the flan falls on the plate, remove the loaf pan. It's all done!