Blueberry Flax Muffins

Preheat the oven to 375°F. Grease a muffin tin; or line it with papers, and grease the papers., Whisk together the flour, flax meal and seeds, baking powder, baking soda, and salt., In a separate bowl, beat the butter and sugar until creamy., Scrape the bottom and sides of the bowl, then add the eggs one at a time, beating well after each addition., Add the vanilla and buttermilk and mix again. The batter may look a bit curdled; that's OK., Add the dry ingredients, mixing on low speed just until the batter is smooth. Fold in the berries by hand., Scoop the batter into the prepared muffin cups, using a heaping 1/4 cup for each; a muffin scoop works well here. Sprinkle each muffin with a bit of coarse white sparkling sugar, if desired., Bake the muffins for 20 to 25 minutes, until a cake tester inserted in the center of one comes out clean. Remove them from the oven, cool in the pan for 5 minutes, then transfer the muffins to a rack to finish cooling., Yield: 12 muffins.