Preheat oven to 325º F and line a muffin tin with 12 paper liners.
In a medium bowl, whisk together the almond flour, cornstarch, baking powder, and salt until combined.
In a separate bowl, add the eggs, honey, melted coconut oil, vanilla extract and apple cider vinegar. Whisk until combined.
Add the dry ingredients to the wet ingredients. Stir until no more streaks of almond flour remain, then gently fold in the chopped blackberries.
Spoon the batter into the prepared muffin tin, then bake for 22-25 minutes or until a toothpick inserted in the center comes out clean. Let cool before serving.
The muffins will turn a golden brown color early on. To test for doneness, do not rely on the color; instead stick a toothpick into the center of a muffin and if it comes out clean with some dry crumbs, the muffin is ready. You can also test it for doneness by pressing the top of the muffin lightly and if it springs back it is done. If a dent is left in the muffin, it needs a few more minutes to finish baking.I find that chopping the blackberries allows the fruit to more evenly distribute into the batter so you get blackberries in every bite rather than a massive blackberry in one bite. Gently fold in the blackberries so the juices don't make your batter light purple. If you are unable to tolerate corn, use tapioca starch and a corn-free baking powder for this recipe. However, cornstarch helps with the overall crumb of the muffin, reducing the overall grainy texture and producing a fluffy muffin.Don't skip the apple cider vinegar because ACV helps baked goods rise. If you don’t have any on hand, you can use white vinegar instead.