Nothing guarantees pure, unadulterated joy like a cupcake. Okay, that's not totally true. There are other surefire ways to achieve pleasure - but nothing quite as innocent or wholesome. Since Glenn Quirion and David Venter opened Sweet Tooth Bakery (371 West Broadway, South Boston, 617.268.2555) last fall, it's become a destination for confectionary connoisseurs far and wide who want to sample the variety of at least seven cupcakes that are made each day. The treasures include berry-cream-filled, red velvet, truffle-topped, lemon-filled, Boston cream, carrot cake, and "make a wish" (crowned with a fortune cookie). But Sweet Tooth hardly limits itself to quick fixes. Quirion, the baker, can prepare a custom-designed wedding cake as breezily as he can whip up a mother lode of fresh chocolate truffles. Cakes and pies are usually available for a last-minute party, and the chocolate pizza gives a whole new meaning to "heat and eat."
