Double strain** over a cocktail glass that's been filled with ice.
Top off the rest of the glass with the grapefruit sparkling water and stir.
Garnish with a grapefruit slice.
Notes
*Don't be intimidated by the beet simple syrup. It's actually quite easy and will only take you a few minutes. Check out the recipe here.**To double-strain, you'll need a small strainer (like this one). Hold the strainer over your glass while you pour the shaken cocktail. This will catch all the raspberry bits. You can omit this step if you don't mind the raspberry seeds in your drink.