My friend and her girl did toast some white rice in a dry pan until lightly golden, then blend it into a fine powder, and store it in an airtight container. When it was time to feed her, I would just cook a small amount of the powder with water or breastmilk over low heat, stirring until it thickened into a smooth porridge. For brown rice it's the same thing, just note that it takes a little longer to cook through since the grain is coarser