1. For the raspberry ripple, simmer the raspberries, sugar and honey in a small saucepot until the raspberries break down, about five minutes. Puree, strain and chill the sauce completely.
  2. For the ice cream, bring the milk, milk powder and lemon zest up to a simmer over medium heat in a saucepot. In a separate bowl, whisk the egg yolks, sugar and salt. Add the hot milk gradually to the egg mixture while whisking constantly, then return this to the saucepot, whisking over medium heat until thickened, about 5 minutes. Strain, cool to room temperature and then chill the custard completely.
  3. Whisk the sour cream into the chilled custard until smooth and then pour this into an ice cream maker, following manufacturer’s instructions. Once frozen, spoon half of the ice cream into a storage container and drizzle half of the raspberry sauce overtop. Use a paring knife or skewer to “ripple” the raspberry sauce throughout (but do not overdo it, in order to keep the ripple distinct). Spoon the remaining half of the ice cream on top and repeat with drizzling and rippling the raspberry sauce. Freeze the ice cream for at least three hours to set, and then scoop to serve.