In a medium bowl, dissolve the rice flour in the water, mixing well to avoid lumps.
In a saucepan, heat the milk over medium heat until it begins to steam, but do not let it boil.
Gradually whisk the rice flour mixture into the heated milk. Continue to cook, stirring constantly, until the mixture thickens (about 5-7 minutes).
Stir in the sugar, vanilla extract, and ground cardamom (if using). Cook for an additional 2-3 minutes, or until the mixture is thick and smooth.
If using, stir in the rose water or orange blossom water.
Pour the mhalbiya into serving dishes or bowls. Allow it to cool slightly at room temperature, then refrigerate for at least 2 hours or until set.
Before serving, garnish with chopped nuts and a sprinkle of ground cinnamon if desired.
Enjoy your meal!