Preheat the oven to 350 degrees F. Taste an extra strawberry for sweetness. This will help you know how much sugar to add later. Add strawberries to a small rimmed baking dish (I used an 8x8 pan). Sprinkle with 1/4 cup sugar and vanilla extract and stir. Roast in oven for 20 minutes.
Meanwhile, add heavy cream and 1/2-3/4 cup sugar. If you strawberries are super ripe and sweet, add 1/2 cup. If they weren't very sweet, add 3/4 cup. Heat over medium low heat, stirring, until bubbles form around the edges of the pan. We just want to dissolve the sugar. Pour heavy cream into a heat safe bowl with a lid and set aside.
Add the roasted strawberries, along with any juices they released, to a blender or food processor. Add whole milk and blend until smooth. Pour into the heavy cream mixture and stir well. Refrigerate until completely cool, 4 hours to overnight.
Once cooled, add to your ice cream machine. Freeze according to manufacturers instructions. During last few minutes of churning, add chopped dark chocolate. Eat right away or store in freezer in airtight containers.