If you’ve ever tried to stay cool on a wilting August day in St. Louis or upstate New York, then you probably know frozen custard. Jennifer Millar does. When the owner of South Berkeley’s Sweet Adeline Bakeshop was making plans to open nearby Addie’s Pizza Pie last year, she sourced the special freezer needed to churn frozen custard — it freezes more slowly, and at a slightly higher temperature than a standard ice cream maker does, yielding a frozen confection with an amazingly smooth texture that feels silken on the tongue. Millar uses a mixture of Clover milk and half-and-half, enriched with organic cream from Straus Family Creamery in West Marin (locavore credentials you’d be hard-pressed to find the equivalent of in St. Louis), in a simple range of classic flavors (vanilla, chocolate, strawberry) that don’t distract from the extraordinary texture of what she’s churning. And unlike the Midwest, where the summer heat index has the power to liquify asphalt, here in mild-climate Berkeley you have the luxury of eating frozen custard slowly, without risk of melting before reaching the end of your scoop.