Boil 4 cups of water in a medium saucepan. Add sago pearls and cook for 10 minutes until translucent. Stir occasionally. Drain, rinse under cold water, and set aside.

In a small saucepan, combine brown sugar and 1/2 cup water. Cook over medium heat for 5 minutes until sugar dissolves and mixture thickens. Remove from heat and add vanilla extract if using. Set aside.

Heat soy milk in the medium saucepan until warm but not boiling.

Divide sago pearls among 4 serving cups. Pour warm soy milk over pearls, filling each cup 3/4 full. Drizzle brown sugar syrup on top.

Serve immediately.