In a large bowl, combine sweetened condensed milk, vanilla and lavender extract. Set aside.
In a food processor, blend blackberries until pureed. Add 1 tablespoon of water and blend a little bit more.
Add the puree to the condensed milk mixture and mix until combined.
In a stand mixer fitted with a whisk attachment, beat heavy cream on medium/high until stiff peaks form.
Fold the whipped cream into the blackberry/milk mixture and mix until combined (1 -2 minutes).
Line a bread pan with parchment paper and pour blackberry mixture into pan. Freeze over night.
If you want, once the ice cream is frozen, you can drizzle purple melting chocolate over the top.