Combine ingredients in a small saucepan and set over medium heat. Bring to a simmer and let reduce 30 minutes, making sure to occasionally stir or whisk the mixture. Strain through a sieve into a container with an airtight lid (to avoid any moisture buildup, which can lead to mold), discard pandan leaves, and let the condensed milk completely cool down. We recommend letting it sit in the fridge overnight. Separation is natural, so make sure to blend or whisk the final product before combining with the phín-filtered coffee.