Oh! Well, happy birthday, Miss Platina! [He'll let that "commoners" comment slide momentarily.]

I wish I had known it was your birthday sooner, I would've been more than happy to bake a cake for you as a gift. [Still would be, if she wanted.] As for your question, I'm sure birthdays can be celebrated however you wish--either with a small cake for a simple affair or putting together something as elaborate as a full spread of treats if one like's to have a celebration with an extravagant flavor. It's all a matter of one's tastes, I suppose, not just due to one's social status.