Start by breaking the red gulaman bars into small pieces and place them in a large saucepan. If you're using gulaman powder instead, simply pour it into the pan. Add the water, pineapple juice from your canned pineapples, and sugar. Turn your heat to medium-high and bring everything to a boil.
Once boiling, lower the heat to medium-low and simmer for 15 minutes. Keep stirring occasionally until you can't see any gulaman pieces anymore. If you lift your spoon, the liquid should run clear without any particles.
Take your pan off the heat and stir in the evaporated milk and vanilla extract right away. Let this cool for 5 minutes, giving it a gentle stir now and then to prevent a skin from forming on top. The mixture will start to thicken slightly.
When the mixture has cooled a bit but is still easy to pour, add your pineapple chunks and raisins. Pour everything into your mold or container. Here's a helpful tip: rinse your mold with cold water first – this will make it easier to remove the gulaman later.
Let it cool on your counter for about 15 minutes, then put it in the refrigerator. Leave it there for at least 4 hours or overnight. You'll know it's ready when it feels firm to the touch and doesn't wobble when you tilt the container.
When you're ready to serve, run a knife around the edges of your mold. Dip the bottom quickly in warm water for 10 seconds, then turn it over onto your serving plate. If it sticks, gently tap the bottom of the mold. Serve it cold.
Keep your gulaman covered in the refrigerator and enjoy it within 5 days. If the surface starts to look dry, just cover it with plastic wrap.
Remember: This recipe is pretty forgiving – the most important thing is making sure your gulaman is completely dissolved before adding the milk. Even if it's not perfect the first time, it'll still taste delicious!