I have to agree with Dan that I prefer some lemon or lime juice to balance out sweet flavors. I've tried a lychee martini with just vodka and lychee juice with a canned lychee garnish, and I didn't like the flavor. A Vieux Mot is much tastier in my opinion. St Germain really does have a nice lychee flavor to it. A softer gin like Plymouth or Bluecoat should go nicely with the lychee flavors, but you could always swap it out for vodka if you prefer.
If you still want to go the vodka + lychee juice or liqueur route, I would add at least 1/2 oz of fresh lemon or lime juice to balance things out. Just like better Cosmos use fresh lime juice.
I would think that the presence of gin takes away from the lychee and can overpower it. Granted this wouldnt be a true martini but how many "tini's" actually are true martini's nowawdays. I've only had this once or twice but I'm pretty sure the recipe for it was equal parts soho lychee liquor and vodka, a dash of lychee juice. Mix well and strain into a cocktail glass and top off with a piece of lychee inside. :D
A very high quality cocktail which tastes like lychee was created by bar manager Don Lee of PDT (Please Don't Tell), in NYC. The Vieux Mot (old witty saying) combines gin, elderflower liqueur, and lemon. There is no actual lychee in it, but the complex flavors of elderflower liqueur really taste like lychee. This is a fascinating drink, much, much better than the lychee "Martini" recipes I found on line. The full cocktail and attribution is in Kindred Cocktails, but here's the recipe:
1 1/2 oz Gin, Plymouth (although I use other gins)
1/2 oz Elderflower liqueur, St. Germain
3/4 oz Lemon juice
1/4 oz Simple syrup
Shake, strain, straight up, cocktail glass
The St. Germain liqueur is pretty widely available these days. It is made of the delicate elderflower, harvested once a year. I suggest keeping the bottle in the refrigerator to prolong its fragrance and freshness.
For the more adventurous, the Bitter Elder is very similar, but contains a touch of Campari. And I adore the name.
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