Microwave 1 (4-oz.) white chocolate baking bar, chopped, in a 2-qt. microwave-safe bowl at HIGH 1 minute or until glossy. Let stand 5 minutes; stir just until melted and smooth. (Do not overstir or chocolate will lose its gloss and firm up.)
Spoon into a zip-top plastic freezer bag. Snip 1 corner of bag to make a small hole. Pipe chocolate onto parchment paper, using stencil as a guide.