Place brownies on a wire rack set over a baking sheet.
Microwave jam in a glass measuring cup on HIGH 10 to 15 seconds or just until slightly melted; stir until smooth. Stir in liqueur, if desired. Pour a small amount of jam into a flavor injector; inject each brownie through the side with a small amount of jam. Refill injector as needed until all brownies are filled.
Microwave pourable frosting in original container on HIGH 20 seconds. Pour or spoon frosting over brownies. If additional frosting is needed, scrape off excess frosting from baking sheet, and reheat.
Microwave white chocolate morsels in a glass measuring cup on HIGH 1 minute or until melted, stirring after 30 seconds. Place white chocolate in a zip-top freezer bag. Snip a tiny hole in 1 corner of bag; drizzle melted white chocolate over brownies. Chill brownies 30 minutes or until chocolate is firm.
Note: Look for plastic flavor injectors in the kitchen gadget section at Wal-Mart.