Preheat the oven to 350°F (180°C, or gas mark 4) and line a 12-cup muffin pan with paper liners.
To make the muffins: In a large-size bowl, combine the almond flour, arrowroot starch, cinnamon, baking powder, and sea salt. In a separate small-size bowl or mixing cup, combine the eggs, honey, and vanilla. Add the wet mixture to the dry ingredients, mixing just enough to combine, then gently fold in the blueberries.
To make the topping: In a small-size bowl, use your fingers to crumble together the topping ingredients.
Divide the muffin batter evenly among 12 muffin cups. Top each with crumb topping. Bake for 35 to 40 minutes, or until a toothpick inserted into the center comes out clean. As soon as the muffins are cool enough to handle, transfer them to a rack and allow to cool before serving.