This is a fun drink to experiment with. For example, you could use half the cassis in the shaker, make the drink, then drizzle the remaining cassis into the drink over the twists of a bar spoon. You will get a purple haze that slowly dissolves and has a rather interesting look.
The earliest known reference to the El Diablo cocktail is found in Trader Vic’s Book of Food and Drink published in 1946 and referred to as the Mexican El Diablo.
It’s a devilish delight.