The sweetness of fresh corn makes it an excellent flavor base for homemade ice cream.
Using a large knife, slice kernels from cobs; place in a large saucepan. Cut or break cobs into thirds; add to pot with milk, cream, and 1/2 cup sugar. Bring mixture to a boil, stirring; turn off heat. Remove cobs, and discard. Using an immersion blender or a blender, puree mixture. Infuse for 1 hour by covering the pan with a tight-fitting lid.
Uncover, bring to a simmer, and turn off heat. In a small bowl, whisk the egg yolks and remaining 1/4 cup sugar. Add a cup of hot cream to yolks, stirring constantly so they do not curdle. Add the yolk mixture to saucepan, stirring. Cook over medium-low heat, stirring constantly, until thick enough to coat the spoon, about 10 minutes.
Pass custard through a coarse sieve, then through a fine sieve or chinois, pressing down on solids; discard solids. Let custard cool. Cover; chill at least 4 hours. Freeze in an ice-cream maker according to the manufacturer's directions. Serve garnished with blackberries.