Preheat your oven to 375 degrees F. This is a crucial step as it ensures your muffins bake evenly and rise beautifully. While the oven heats, line a standard muffin tin with liners or grease it well with non-stick cooking spray to prevent sticking.
In a large mixing bowl, combine flour, sugar, salt, baking soda, and baking powder. Mix these dry ingredients well, ensuring that everything is evenly distributed. This mixture will form the backbone of your muffins.
Add oil, egg, buttermilk, and vanilla to the dry ingredients. Mix gently until everything is just combined. Be careful not to over-mix; the batter doesn’t need to be smooth, and a few lumps are perfectly fine. Over-mixing can lead to dense muffins.
Toss the blueberries in a spoonful of flour before adding them to the batter. This step is optional but helps prevent the blueberries from sinking to the bottom of the muffins during baking. Gently fold the blueberries into the batter, taking care not to break them.
Divide the batter evenly between the prepared muffin cups. Fill each cup about two-thirds full, allowing room for rising. The batter should be slightly lumpy but well-distributed with blueberries.
To make the crumb topping, in a separate bowl, combine the remaining granulated sugar, brown sugar, flour, butter, and cinnamon. Use a fork or pastry blender to cut the butter into the mixture until it resembles coarse crumbs. This will add an irresistible crunch on top.
Sprinkle the crumb topping generously over the muffins before placing them in the oven. This adds a delightful texture and sweetness to the muffins as they bake.
Bake the muffins in your preheated oven for 17 to 20 minutes. Keep an eye on them; they're done when a toothpick inserted in the center comes out clean or with just a few crumbs attached. The tops should be golden brown.
Once baked, remove the muffins from the oven and allow them to cool in the pan for a few minutes before transferring them to a wire rack. This will help prevent them from becoming soggy and will keep the bottoms firm.
Allow the muffins to cool completely on the wire rack. Enjoy them warm, or store them in an airtight container for later. They make for a delicious breakfast or snack any time of day.
