Is this Philly’s most esoteric cocktail bar? You bet your cachaça it is.

I once went to a concert of avant-garde, atonal music: compositions crafted by a group of empirically brilliant young composers, performed improbably (unbearably) by a quartet composed only of saxophonists. As I winced through it, I kept thinking, "A smarter, more sophisticated person would get this. Maybe a person who understands music theory?"

A similar feeling came over me as I sank into one of the plush thrones that pass for barstools at the unrecognizably chic revival of the classic Philly restaurant Friday Saturday Sunday, and peered into a drink called the Paper Trail. It's made with tequila, grapefruit, lime and soda, jumbled with unexpected complements — Bonal, a bitter and herbal French aperitif, and Punt e Mes, a bittersweet Italian vermouth — and served in a sparkling, cut-crystal glass with a sheaf of mint. If I'm being honest, it looked and tasted like a high-class Long Island Iced Tea.

But a Long Island Iced Tea with a pedigree, created by Paul MacDonald, the kind of bartender who's also an amateur cocktail historian with strongly held beliefs, such as: "It's my opinion that the ideal number of cocktails to put on a menu is eight." In his view, that's enough to touch on every flavor profile, without redundancies, while leaving just the right amount unsaid.

"What really drives our program forward are the personalities and relationships with the bartenders. I hate sitting at a bar and being given a book of 50 cocktails. It's like giving someone a bunch of paperwork," he said. He'd rather coax out a visitor's preferences over the course of an evening and offer up something off-menu — for example, a cordial glass of cream-soda-tasting clarified milk punch made with Rhum agricole, lemon juice, strawberries and house-made cardamom shrub.

As a socially awkward person who is, like, really into paperwork, this is my worst nightmare. But, for my second round, I give it a shot. I request something bitter and not too boozy. I end up with a drink called Fire Insurance that reportedly includes rum, gin and red wine; the only nonalcoholic ingredient I detect is the swatch of lemon peel.

I left it on the marble-topped bar and examined the year-and-a-half-old renovation, which is at once cozy, elegant, and quirky. A study in Gothic romance with thick dark draperies, dozens of warmly flickering candles, a black-and-white checkerboard pattern, and a stuffed — and, therefore, unnecessarily caged — crow positioned above the bar like a glassy-eyed familiar.

It was filled with well-heeled, Rittenhouse Square couples on intimate, expensive dates, sipping drinks as they waited for tables at the restaurant upstairs or sampling strikingly composed offerings from the kitchen, like savory slabs of mussel toast arranged along a plank, or eggs and caviar served in the shell atop a torn paper egg carton.

Down at the end of the bar was a group of guys in office-ready button-down shirts. One, presumably a liquor sales representative, passed MacDonald a bottle to sample, saying, "It's really changing the paradigm of what cachaça is."

These men, I thought — they would really appreciate the Fire Insurance.

261 S. 21st St., 215-546-4232, fridaysaturdaysunday.com

When to go: Get there early to stake out one of the comfortable barstools. The bar's open Tuesday through Sunday, 3 p.m.-1 a.m., though kitchen hours are more limited.

Bring: A date you'd really like to impress. Your spouse on a big anniversary. Or, really anyone who has a reference point for the cachaça paradigm.

Order: If you're a Manhattan drinker, try the Drink with No Name ($15), which adds sherry and aquavit to the standard rye-and-vermouth pairing. There's also a tightly curated list of wines by the glass (like the Lebanese Massaya $13) and a selection of draft and bottled beers like a Sly Fox Pikeland Pils ($6). Or, if honestly all this craft stuff just isn't for you? They have a $4 Miller High Life with your name on it.

Bathroom situation: With this level of attention to detail, of course the vintage, black-and-white motif continues into the clean, single-stall bathroom.

Sounds like: Finally, a bar where you can carry on a conversation, with background music — a mix of twangy jazz, funk, and Afrobeat, on a recent evening — setting the vibe at a calm 84 decibels.