1. Preheat the Oven and Prepare the Pan

Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or lightly grease with non-stick spray.

2. Mix the Dry Ingredients

In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and cinnamon (if using). This helps evenly distribute the leavening agents for a uniform rise.

3. Prepare the Wet Ingredients

In a separate bowl, whisk the egg, buttermilk, vegetable oil (or melted butter), and vanilla extract until well combined. The buttermilk adds acidity, which reacts with the baking soda to create light, airy muffins.

4. Combine Wet and Dry Ingredients

Make a well in the center of the dry ingredients and pour in the wet mixture. Gently fold everything together with a spatula until just combined. Avoid overmixing—a few lumps in the batter are okay and help keep the muffins tender.

5. Fold in the Raspberries

Gently fold in the raspberries using a spatula. If using frozen raspberries, do not thaw them before adding, as they can release excess moisture. Tossing the berries in a tablespoon of flour before adding can help prevent them from sinking to the bottom.

6. Prepare the Streusel Topping (Optional)

In a small bowl, mix flour, sugar, and melted butter until the mixture resembles coarse crumbs.

7. Fill the Muffin Cups

Divide the batter evenly among the muffin cups, filling each about ¾ full. Sprinkle the streusel topping over each muffin if using.

8. Bake the Muffins

Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean.

9. Cool and Serve

Allow the muffins to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely. Enjoy warm or at room temperature!