Step 1: Preheat your oven to 375°F (190°C) and line your muffin tin with muffin liners or lightly grease the cups.

Step 2: In a large mixing bowl, whisk together the dry ingredients: flour, sugar (both granulated and brown), baking powder, salt, and cinnamon (if using).

Step 3: In a separate medium bowl, whisk together the wet ingredients: egg, melted butter, milk, vanilla extract, and lemon zest (if using).

Step 4: Gently fold the wet ingredients into the dry ingredients using a rubber spatula or wooden spoon. Stir until just combined. Be careful not to overmix, as this can result in dense muffins.

Step 5: Gently fold in the blueberries. If you’re using frozen blueberries, you can toss them in a little bit of flour to prevent them from sinking to the bottom.

Step 6: Spoon the muffin batter evenly into the muffin tin, filling each cup about 3/4 full.

Step 7: Bake in the preheated oven for 18-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.

Step 8: Remove the muffins from the oven and let them cool in the tin for about 5 minutes before transferring them to a wire rack to cool completely.