Sweet Corn Ice Cream

1. Using a large knife, slice the kernels off the corn cobs and place in a large saucepan. Break cobs in half and add to pot along with milk, cream and 110 grams (1/2 cup) sugar. Bring mixture to a boil, stirring, then remove from heat. Let stand to infuse for 1 hour, then discard corn cobs.
2. Using an immersion or regular blender, puree kernel mixture. Return mixture to a simmer, then turn off heat. In a small bowl, whisk egg yolks, 1/8 teaspoon salt and another 55 grams ( 1/4 cup) of sugar. Add a cup of hot cream mixture to yolks, stirring constantly so they don't curdle. Add yolk mixture to saucepan, stirring. Cook over medium-low heat, stirring constantly, until custard thickens enough to coat the spoon, about 10 minutes.
3. Pass custard through a fine sieve, pressing down hard on the solids. Discard solids. Whisk in sour cream until smooth. Let custard cool in an ice bath, then cover and chill for at least 4 hours.
4. Meanwhile, in a small saucepan, combine remaining 60 grams sugar (5 tablespoons), lemon verbena (or zest) and 1/4 cup water and bring to a simmer. Let cook, stirring occasionally, until sugar melts and syrup thickens slightly, about 7 minutes. Add blackberries and cook for 5 to 7 minutes longer, until fruit just softens, but doesn't fall apart. Let cool, then discard verbena.
5. Freeze corn mixture in an ice cream maker according to manufacturer's directions. Serve with blackberries and syrup on top.