I love the basic Tom Collins format of gin + lemon + simple syrup + soda water -- it's easy to riff on, and has the added bonus of letting you call the resulting drink "a (Something) Collins," which conjures up a speakeasy boozy vibe, like tough Old New York, rather than a girly fruity cocktail (which, in actuality, most of my variations are).
This drink was developed based upon the available fruit/booze/herbs in our cabinet and garden. In general, I tend towards cocktails that are sweet and citrusy, and while this drink has both elements, the herbs and cucumber keep it from being cloying, making it as refreshing as a dip in the pool. —deensiebat
First, prepare the basil syrup: toss the basil leaves, lemon zest, sugar, and water in a small saucepan. Bring to a boil, then remove from heat and allow to infuse for half an hour (if you've got the time -- and longer won't hurt). Strain, discarding the leaves and peel and reserving the syrup.
Next, make a raspberry puree: blend the raspberries, lemon juice, and a healthy splash of the basil syrup in a blender until pureed. Strain if desired, or leave the seeds in if you don't mind.
To assemble the drink, mix together a shot of gin, a shot of raspberry puree, and about 3/4 shot of the basil syrup. Shake, then pour into a glass with plenty of ice. Top with an equal amount of soda water, toss in a few slices of cucumber, and taste, adjusting the balance to your drinking preference. Drink poolside, languorously.