Prepare Blueberry Purée: Place the blueberries in a blender or use an immersion blender to process them until completely smooth. This purée will infuse the ice cream with fresh, vibrant berry flavor. Set aside the purée while you begin working on the base.
Combine and Heat Dairy Mixture: In a medium to large saucepan (about 4 quarts), combine 2 cups of whole milk, the heavy cream, blueberry purée, sugar, corn syrup, and salt. Whisk these ingredients together over medium heat, stirring occasionally, until the mixture is heated through and just begins to boil.
Prepare Cornstarch Slurry: While the milk mixture warms, whisk together the remaining 2 tablespoons of milk with the cornstarch in a small bowl until smooth and free of lumps. This slurry will thicken the ice cream base.
Thicken the Ice Cream Base: Once the dairy mixture reaches a rolling boil, continue boiling for about 60 seconds to activate the thickening process. Remove the saucepan from heat, and gradually whisk in the cornstarch slurry. Return the pan to medium heat and bring back to a gentle boil, stirring constantly, until the mixture thickens noticeably.
Infuse Lavender and Vanilla: Take the pan off the heat and stir in the vanilla extract. Add the dried lavender buds and cover the pan. Let the lavender steep in the warm base for 20 minutes to impart a delicate floral aroma.
Strain and Chill the Base: Strain the mixture through a fine mesh sieve into a clean container to remove the lavender buds and any lumps. Cover the container tightly and refrigerate the base for 6 to 8 hours, or overnight, to chill thoroughly and develop flavors.
Churn the Ice Cream: Once chilled, pour the base into your ice cream maker and churn according to the manufacturer’s instructions, usually about 25 minutes, until the mixture reaches a soft-serve consistency.
Freeze Until Firm: For firmer ice cream, transfer the churned ice cream to an airtight container and freeze for 4 to 6 hours before serving. Enjoy immediately for a creamy, soft-serve texture.