Preheat and Prepare
Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or lightly grease it with non-stick spray.
Mix Dry Ingredients
In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
Mix Wet Ingredients
In a separate bowl, whisk together the buttermilk, melted butter, egg, and vanilla extract until well combined.
Combine Wet and Dry Ingredients
Gently fold the wet ingredients into the dry ingredients using a rubber spatula, stirring until just combined. Be careful not to overmix to avoid dense muffins.
Add Raspberries
Gently fold in the raspberries, making sure to coat them lightly with flour to prevent them from sinking to the bottom of the muffins.
Fill Muffin Tin
Spoon the batter into the muffin tin, filling each cup about 2/3 of the way full.
Bake
Bake in the preheated oven for 18–22 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs.
Cool and Serve
Allow the muffins to cool in the tin for 5 minutes, then transfer them to a wire rack to cool completely. Serve warm or at room temperature.