This is a missable achievement and considering many walkthroughs specify only the essential items for the main quest, you might miss the item for this missable achievement.

The "Super-charged Potpourri Easter Egg" Achievement requires you to pick up flowers at Fleur's shop almost before the end of part 1.
At the Cave you need to combine:

• Wood shavings
  
• Eau de Toilette
  
• FLOWERS

In case you missed that item you can grab my save file!

https://1drv.ms/u/c/0a191ba56432d689/EYnWMmSlGxkggAoIGAAAAAAB_s85Ng69LTK43XktisaYbQ?e=nsEqsT

Here is my savefile. Just extract it and replace in "Documents\Broken Sword 5" folder.
Launch the game and Load the "second-last" save file (it should be the 7th entry, not counting the autosave).

You will be right in the cave with everything done already, just prepare the potpourri and you can go on already with the adventure!