In a 2 qt. saucepan, heat together milk, cream, lavendar, vanilla bean and seeds, salt, and 7 ounces of the sugar, stirring to dissolve sugar. Bring just to a simmer, remove from heat and steep 30 minutes.
Strain mixture through a sieve, cover, and refrigerate until cold, 6 hours or overnight.
Preheat oven to 400 degrees F. Cut peaches in half, removing pits. PLace skin-side down on a parchment-lined baking sheet. Sprinkle 1 oz. sugar over flesh evenly. Roast until soft and golden, about 15-20 minutes. Cool to room temperature.
Peel peaches and coarsely chop, reserving any juices.
Pour cream base into an ice cream maker and process according to manufacturer's directions. Add peaches and reserved juice during last minute of churning to just combine.
Extract ice cream into a container, press parchment directly on top, and freeze solid, preferably overnight.