With an immersion blender, beat the eggs until they are light and foamy. This takes about a minute.
Slowly add in the sugar and brownie mix, until well incorporated. (About two minutes)
Add vanilla.
In a large measuring bowl, mix together the cream and milk. Gently stir in the egg mixture. (you don’t want to beat it at this point, the air is already added to the eggs)
Pour into your ice cream maker and make according to your maker’s directions.
Notes
If you would like to heat treat the brownie mix, there are instructions in the post.