Grape-nut, Indian pudding, ginger — this is an ice cream shop that knows its audience. No wonder the lines get so long on hot days. These classic New England flavors are just a handful of dozens that rotate through the menu here. Another excellent choice: the dark chocolate “Bishop’s Bash,” loaded with chocolate chips, nuts, and brownie chunks. Rounding out the offerings are “Bish-Burger” ice cream sandwiches, frappes, sundaes, and sorbet. For New Hampshire natives, it’s the taste of summer.