The one and only time I vacationed in the Bahamas, I had to do a double take as I checked out of my hotel: At the bar was the balding, tan, Hawaiian-shirt-clad Jimmy Buffet, nursing the drink synonymous with his name. It was barely 11 a.m.

Unlike Mr. Buffet, I don't order (or make) margaritas when it's hot and sunny; rather, due to synaptic miswiring or an off-kilter sense of time, I crave them when the first autumn chill shows itself in late summer. When a few rogue leaves begin changing on the trees, I feel like sipping something with a little sourness, something that looks and feels cheerful to order but portends sharper times to come. And sour mixes and triple sec and frozen versions be damned -- they should never be too sweet, or too easy a drink to make.

Even though this very American drink is usually constructed on a holy trinity of tequila, lime juice and orange liqueur, margaritas are a blank canvas on which you can impose any triad of flavors, provided you maintain the sweet-sour aspect and tequila base.

Currants, for instance. At South Hero's Blue Paddle Bistro this week, a bag of fresh currants lurked behind the bar. Eaten by themselves, they're tart to the point of pain. Yet when Marc Champoux, a veteran mixologist and Blue Paddle's bar manager, muddles some and adds fresh lime juice, simple syrup, silver tequila and Cointreau, he captures the essence of late summer in a glass. (And, for the non-margarita-inclined, Marc has a drink specials list that makes it worth driving to the islands for just a cocktail.)

My senses alight, I began seeking creative margaritas all over the place. At El Gato Cantina, the new Mexican eatery on lower Church Street, the staff infuse their own tequila with things like pineapple and hot peppers. Here, I partook of a coral-colored grapefruit margarita (served in an old-fashioned glass) made with jalapeño-infused silver tequila; it had a naughty little kick at its core.

The Bearded Frog in Shelburne concocts a moodier version in its dim, perpetually autumnal bar: its St. Germain margarita is bright, herbaceous and feels very 1940s in your palm. For an extra dose of bitterness, ask for the version topped with Campari.

The most creative frontier, though, is home. SInce a friend of mine recently waxed poetic about a watermelon-jalapeño margarita she had during her summer vacation, I became determined to render one myself. Instead of jalapeños, though, I infused simple syrup with serrano chilis, giving it a gentle but noticeable heat. The watermelon pureé is summer itself, and though I tried this with fresh orange juice, Cointreau really has presence; though it's expensive stuff, you can buy tiny bottles of it at some liquor stores.

I'm a resolute non-measurer when cooking or mixing, so you can follow these amounts loosely. I also think in cups and tablespoons, rather than ounces.

Watermelon-Chili Margarita

1/2 serrano chili, sliced
2 tbsp. white sugar
2 tbsp. water
3/4 cup of watermelon chunks 
2 limes
1/3 cup silver tequila (preferably 100% blue agave)
a generous glug of Cointreau 

First, make a simple syrup by combining the sugar, water and the chili in a saucepan, and bring to a simmer. Once the sugar is dissolved, remove from heat and let sit for at least a half-hour.

Pureé watermelon chunks in a blender or food processor until soupy (you should end up with about 1/2 cup of pureé). Add purée to a shaker with tequila, Cointreau, simple syrup and juice from both limes (use only one for a sweeter drink). Shake vigorously. Rub cut lime around the edge of a lowball glass, and drag its rim through a plateful of kosher salt, then fill with ice. Pour watermelon slurry over ice, and waste away again.