A quick heads-up before diving into the story: I've set aside for you a complete shopping list of every ingredient you'll need so you can recreate this classic at home. Here's the tale.
The Mimosa was born in Paris in 1925, at the bar of the legendary Ritz Hotel, created by bartender Frank Meier. Meier, of Austrian origin, was one of the most famous bartenders of his era, and named the drink after the tropical mimosa flower, whose yellow color perfectly matched that of the cocktail. An almost identical predecessor, the Buck's Fizz, had appeared in London in 1921 at Buck's Club.
The Mimosa became the Sunday brunch drink par excellence throughout the 20th century, especially in the United States, where it conquered American hotels in the 1960s. It's one of the few cocktails considered socially acceptable to drink in the morning — a small license to weekend luxury, born in the heart of Belle Époque Paris.
To recreate this one with the right style, tools matter as much as the recipe. I use and recommend a complete barman kit like this set on Amazon, which covers every essential tool at a very reasonable price. For a more serious setup, a professional cocktail bar station keeps bottles, glasses and tools organized and close at hand, instantly upgrading the whole experience.