Place glutinous rice in a fine strainer and rinse under cold water for 30 seconds.

Heat your saucepan over medium-high heat and add the rinsed rice without any liquid. Toast for 2 to 3 minutes, stirring constantly.

Pour 4 cups of water into the saucepan with the toasted rice and bring the mixture to a rolling boil over high heat.

Reduce the heat to medium or medium-low and simmer uncovered for 12 to 15 minutes, stirring occasionally.

While the rice cooks, combine cocoa powder, cinnamon, nutmeg, and brown sugar in a small bowl. Add 1/2 cup of warm water and whisk until smooth.

Once the rice is tender, slowly pour the chocolate mixture into the saucepan while stirring constantly.

Continue cooking over medium-low heat for another 3 to 5 minutes, stirring frequently.

Remove from heat and stir in evaporated milk and vanilla extract if using. Adjust sweetness if necessary.