Preheat the oven to 425°F/220°C. Line a muffin pan with 12 liners.
Whisk together the flour, baking powder, baking soda, salt, and cinnamon in a medium bowl or jug.
In the bowl of a stand mixer fitted with the paddle attachment, add the sugar, butter, eggs, vanilla and buttermilk then beat on medium speed. It is going to be lumpy which is fine!
Pour the dry ingredients into the wet and beat until combined on low speed. Increase the speed to medium and beat until the muffin batter is almost smooth.
Keep a handful of blueberries to the side, then fold in the remaining berries and chocolate chips.
Fill the liners to the top with the batter. Sprinkle over the remaining blueberries on top.
Bake for 5 minutes. Then, without opening the door, reduce the oven temperature to 350°F/175°C and bake for an extra 16-18 minutes.
Allow them to cool completely.
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients about 2 hours before you start baking. Salt: If you don't have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt.Butter: I use European style butter, like Kerry Gold, in my recipes. This will make your finished bake much creamier and richer.Buttermilk: if you don't have buttermilk you can use full fat yogurt or sour cream instead. Storage: keep in an airtight container at room temperature for 2 days, or in the fridge for five days. Freezing: freeze baked and cooled muffins in a freezer bag for up 3 months. Let them thaw in the fridge or at room temperature.