In a large saucepan, whisk together the milk, 1 cup of the cream, egg yolks, sugar, lemon zest, lemon curd, and lavender.
Over medium heat, whisk the mixture constantly, just until it starts to steam, but don't let it come to a boil. Remove from the heat.
Pour the mixture into a lidded container, and refrigerate until well chilled and to allow the flavors to develop, preferably overnight. When you're ready to churn your ice cream, pour the mixture through a mesh strainer to remove the lavender and lemon zest.
Use an electric mixer to whip the remaining cup of heavy whipping cream until soft, thick peaks form. Whisk the whipped cream and the limoncello or vodka into the lemon custard.
Churn the custard in your ice cream maker according to the manufacturer's instructions, until it's a soft serve consistency.
In a bowl, vigorously whisk the raspberry jam to loosen it up into a drizzly consistency.
Spread half the ice cream into a container with at least a 2-quart capacity, and drizzle with half the jam. Repeat with the rest of the ice cream and jam, then use a knife to gently swirl the jam in, leaving visible streaks of jam throughout the ice cream.
Freeze until firm enough to scoop, at least 8-10 hours, or overnight.
Notes
Homemade ice cream can be frozen for about 2 weeks.The limoncello is optional, but the addition of a little alcohol helps to keep the ice cream smooth and creamy.