Preheat the oven to 425°F/220°C. Line a 12 muffin pan with paper liners.
In a small bowl, mix together the all-purpose flour, baking powder, and salt. Set aside.
In a large mixing bowl add the melted butter, granulated sugar, eggs, lemon zest, buttermilk and vanilla. Mix it all together until combined.
Fold in the dry ingredients with a rubber spatula.
Add in the blueberries and white chocolate chips and gently fold them in. If using frozen blueberries, give them a quick rinse first so they don't bleed into the batter.
Divide the muffin mixture evenly over the muffin liners.
Bake the muffins at 425°F/220°C for 5 minutes then turn the oven down to 350°F/180°C and continue baking for another 15-18 minutes or until the tops of the muffins are golden brown and spring back when lightly pressed in the center.
Remove them from the oven and let the warm muffins cool in the pan for 10 minutes before removing and placing them on a wire rack to cool to room temperature.
Notes
The cup sizes are US size, which is smaller than metric. For best results, use scales. *The buttermilk can be substituted with plain yogurt OR 170g of regular milk (¾ cup minus ¾ Tbsp) plus 10g (¾ Tbsp) white vinegar or lemon juice. Mix these two ingredients together before beginning the recipe to let it sit and curdle for 5-10 minutes.