How to Make a Floradora Cocktail
To make your own raspberry syrup, thaw some frozen raspberries; they're cheaper than fresh, and usually loads better too. Put them in a fine-mesh strainer, pressing to separate the juice from the solids. Discard the solids. Mix equal parts raspberry juice and sugar, stirring well until the sugar has dissolved. Store the resulting syrup in the fridge. It should keep for a week or two; you can get more lifespan by adding a tot of vodka.
If you don't feel like getting messy, modern technology does a very decent job with commercial raspberry syrup. It's almost to the point that you're better off buying it instead of making it. The one to get is good ol' Smuckers, despite the presence of high fructose corn syrup in their recipe. About the only grocery store around these parts to carry their raspberry syrup is Safeway.
Or, there's another raspberry possibility: framboise liqueur, better known to many as Chambord. Certainly nothing wrong with that substitution.
If you are making these to impress a 5-foot-4 brunette (or whomever you prefer), you may wish to make a Floradora Imperial. The reasoning behind the variation is simple: Cognac was much more expensive than gin back in those days, so the Imperial uses cognac instead of gin. When I make these, I might also switch out the lime juice in favor of more cognac-friendly lemon.
If you substitute raspberry liqueur for the raspberry syrup, you might want to reduce the gin by a corresponding amount. Or you might want to keep it the same.
2 ounces London Dry gin
1/2 ounce lime juice
1/2 ounce raspberry syrup (or raspberry liqueur such as Chambord)
Spicy ginger ale to fill
Shake gin, lime juice, and raspberry syrup with ice cubes. Pour unstrained into a Collins glass. Top up with ginger ale, stirring gently to combine. Garnish with a lime wedge.
Variation: To make a Floradora Imperial, substitute cognac for the gin.