Kristin Cavallari's twenties included an engagement, a wedding, three precious kiddos and, of course The Hills. And now the MTV alum is closing the chapter on this life-changing decade and is officially a member of the thirties club. It's ON, 3-0!

The Laguna Beach lady shared a glimpse of how she is commemorating this special occasion -- and her morning festivities appropriately included a sweet treat.

"Birthday breakfast cupcakes...why not!" K-Cav captioned the Instagram image above, which finds the b-day gal with a delicious-looking dessert. "#ByeBye20s #Hello30s."

The shoe designer also took to Twitter to express her gratitude for all of the nice messages.

Be sure to wish Kristin a happy birthday in the comments -- and because it's her big day, relive her most epic Hills zingers in the mashup video below!