In a medium bowl, whisk together 1¾ cups white whole wheat flour, 1 tablespoon baking powder, and ½ teaspoon sea salt. Set this dry mixture aside.
In a separate large bowl, stir together ¾ cup coconut sugar, ½ cup + 2 tablespoons Bulgarian-style buttermilk, ½ cup full-fat plain Greek yogurt, ¼ cup melted coconut oil (room temperature), 1 egg, 1 egg yolk, and 2 teaspoons vanilla extract until combined. (Do not add the blueberries, the remaining ½ teaspoon flour, or the 1 tablespoon cane sugar yet.)
Add the reserved dry flour mixture to the wet ingredients. Gently whisk or fold the batter about 8–12 times, just until the flour is moistened. The batter should still show a few flour streaks and have small lumps—do not overmix.
In a small bowl, toss 1 cup fresh blueberries with the remaining ½ teaspoon white whole wheat flour until evenly coated.
Gently fold the floured blueberries into the batter until they are evenly distributed. Fold only until combined to avoid crushing the berries.
Cover the bowl and refrigerate the batter for 1 hour to help the muffins develop domed tops during baking.
After chilling, preheat the oven to 450°F and generously spray or grease a muffin pan.
Use a large ice cream scoop to portion the batter into the prepared muffin tin, filling each cup most of the way full. Sprinkle the tops of the batter with 1 tablespoon raw organic cane sugar.
Bake at 450°F for 5 minutes. Without opening the oven door, reduce the oven temperature to 375°F and bake an additional 15–16 minutes, or until the muffin tops are golden brown and a toothpick inserted into the center comes out clean.
Let the muffins cool in the pan for 10 minutes, then transfer them to a cooling rack to cool completely before serving.