For a mocha coffee flavored variation, substitute espresso powder for matcha green tea powder, and dark chocolate for white chocolate.
In a saucepan, combine sushi rice, 2 1/4 cups of water, sweetened condensed milk and salt. Bring to boil; reduce heat to low. Cover and cook for 25 to 30 minutes or until rice is tender and most of the liquid is absorbed. Let stand, covered, for 10 minutes.
Stir in matcha green tea powder and vanilla. Let stand at room temperature, covered, for about 1 hour or until cooled and thickened.
Roll tablespoonfuls into balls; place on parchment paper-lined tray.
Place melted white chocolate in bowl; using 2 forks, dip balls into melted white chocolate, letting excess drip back into the bowl. Transfer to clean parchment paper-lined baking sheet. Refrigerate for about 15 minutes or until chocolate is hardened.