Stepping into this Mission District parlor seems like a blast from the past. But the rich, custardy ice creams Humphry Slocombe produces are hip and as irreverent and fearless as the owners, who launched the shop in 2008. Sit down at the Formica counter and try Secret Breakfast with toasted cornflakes and bourbon, Elvis (The Fat Years) with banana and peanut brittle, or Government Cheese (over apple pie).