Place the blueberries, balsamic vinegar and maple syrup in a small sauce pot. Bring to a boil then reduce and simmer until the blueberries have broken down. Stirring occasionally while cooking, about 10-15 minutes.
Add the garlic, shallots and red pepper flakes, stir and continue cooking for 5-7 more minutes.
Use an immersion blender (alternatively, you can pour into a regular blender) to blend the ingredients in the pot until desired consistency (I prefer a smoother BBQ sauce as it's easier to coat the meat with).
Return pot to heat, add molasses and season with salt and pepper to taste. Stir and let simmer over low heat for another 15 minutes. Remove from heat and set aside, BBQ sauce will thicken as it cools.
Preheat grill. Rinse and pat dry turkey legs. Season with salt and pepper.
Place turkey legs on the grill once hot. Coat with BBQ sauce as the legs cook, making sure to flip and coat a few times during the process. Cook until internal temperature of the legs is 175 degrees F.