• Preheat the oven to 400 degrees F. Place the plums in a 9 x 9-inch baking dish or casserole dish. (I found this better than a baking sheet because of how much juice is released from the plums.) Sprinkle plums with brown sugar and a few pinches of salt. Roast the plums for 20 minutes and until they're completely tender with a fork and a lot of juice has been released. Remove from the oven and allow to cool for about 5 minutes.
• Add 2 cups heavy cream, sugar, honey and vanilla extract to a saucepan. Heat until sugar is dissolved, about 2-3 minutes. Add 1/4 cup of cream mixture (you can eyeball this measurement) to the jar of a blender, along with the roasted plums and their juices. Blend until very smooth, about 1 minute. Place a sieve atop a large bowl and pour the puree through it, discarding the pulp. Add the remaining milk to the bowl and mix until thoroughly combined. Cover the bowl with plastic wrap and refrigerate until very cold, at least 4 hours of overnight.
• Churn the mixture in the bowl of your ice cream maker, according to your ice cream maker's instructions. Serve immediately for soft serve or alternatively transfer to a freezer-safe container and freezer overnight.

*The type of plums that will give you this beautiful purple color are called Black Splendor plums. They have a purple exterior with a red and purplish flesh.