About 20 guests – including bridesmaids, family and friends – celebrated Ashlee Simpson
's impending marriage to Evan Ross with a "bohemian pool party" at big sister Jessica Simpson
's L.A. home.
"Someone was on hand to help all the guests make flower wreaths," a source told PEOPLE. "The bridesmaids picked a throwback photo to decorate the cake," they added.
Below, the cake in question, featuring what definitely qualifies as a "throwback photo" of Ashlee, 29.
Jessica, 34, posted the next pic with the caption "all the beauties celebrating Ashlee!!! I love you Ash :)" (The fashion mogul herself wed Eric Johnson last month
Jessica also posted a picture of herself posing in a black one-piece swimsuit with a friend, captioned with "#hardworkpaysoff." It does indeed.