In large microwavable bowl, measure cereal; set aside. Line cookie sheet with waxed paper or foil.: The air fills with the faint cardboard cereal scent as you pour Rice Chex into a roomy microwavable bowl, and that first pour is oddly satisfying, a crisp rustling sound. Use a bowl large enough to toss comfortably, so the glaze does not spill when you stir. Lay out waxed paper or foil on a cookie sheet to catch the soon to come drizzle, which makes cleanup effortless. If your bowl is too small, you risk uneven coating and spillover, so give yourself ample space. A common misstep is measuring by eye and ending up with too little cereal for the glaze, which affects balance.
In 2-cup microwavable measuring cup, microwave butter uncovered on High 30 seconds or until melted. Add granulated sugar and water; microwave uncovered on High 30 seconds or until mixture is heated and can be stirred smooth. Stir in vanilla. Pour over cereal, stirring until evenly coated.: The kitchen will smell warmly of melted butter and sugar as you heat them, a scent that signals the start of transformation. When the mixture is warm and glossy, the granulated sugar should dissolve into a syrupy liquid, and stirring should yield a smooth consistency. Adding vanilla at the end preserves its fragrance, so stir it in off heat. Pouring the glaze over the cereal should look like a thin, even veil; use a spatula to fold rather than smash, which helps keep the cereal pieces intact. If the sugar has not fully dissolved, the coating will feel grainy, so reheat briefly if needed. Avoid overheating the butter until it browns, because that will change the flavor profile.
Microwave uncovered on High 4 minutes, stirring every minute, until thoroughly glazed. Sprinkle with powdered sugar; mix well.: As you microwave in short intervals, you will hear gentle bubbling and notice the glaze thicken and cling to the cereal, producing a soft crackle when stirred. Stirring every minute ensures even heat distribution and prevents hotspots that can burn the mixture. After the final stir, dust with powdered sugar , which should cling and create a light, snowy coating. The powdered sugar also absorbs any excess oil, helping the mix reach a pleasant crispness. Watch closely to avoid scorching, and do not skip the minute by minute stirring or you may end up with sticky clumps.
Spread on cookie sheet. In small microwavable bowl, microwave white chocolate uncovered on High 30 to 60 seconds, or until it can be stirred smooth. Place in small resealable food-storage plastic bag; cut off small corner of bag. Squeeze bag to drizzle white chocolate over snack mix; sprinkle with edible glitter. Cool until white chocolate is set, about 10 minutes.: Spreading the warm mix across the lined cookie sheet lets it cool evenly, and you should notice a subtle cooling hiss as steam escapes. Melt the white baking chocolate gently until it becomes silky and glossy, stirring to smooth any lumps. Transfer to a resealable bag for controlled drizzling; a tiny corner cutout yields delicate ribbons. The melted chocolate should be warm but not hot, so it glides without pooling. If the chocolate overheats, it can seize and become grainy, so microwave in short bursts and stir frequently. Working quickly here ensures the drizzle sets with a pleasant sheen.
Squeeze bag to drizzle white chocolate over snack mix; sprinkle with edible glitter. Cool until white chocolate is set, about 10 minutes.: The act of drizzling is tactile and visual, a soft, rhythmic squeeze that creates thin white ribbons across the crunchy landscape. As the white baking chocolate meets the slightly warm mix, it begins to set into a delicate shell, offering a creamy counterpoint to the crisp Rice Chex . Immediately sprinkle the colored edible glitter so it adheres to the wet chocolate, adding shimmer and tiny bursts of texture. Let the tray rest undisturbed for around 10 minutes so the chocolate firms up; touching too soon will mar the finish. One mistake is applying sprinkles after the chocolate is set, where they will not stick, so time this step while the drizzle is still tacky.