Possible Clues:

• Decorating attic in grubby clothes
• It might read "Happy Birthday!"
• Here in Paris nobody goes for starters of some cake
• Cake decorator's supply
• Sea spray that freezes on contact with ships
• Improving cake, including nice gloss initially
• Hard to leave Confucian classic, which is topping
• Medium for a birthday message
• The setter quavers, we hear, getting chilly
• Pastry bag content