When you're ready to make the muffins, turn on the oven and preheat it to 180C / 350F.
Grease a 12 hole muffin tin with butter and set aside.
Whisk together the eggs, melted butter and vanilla until they are well combined.
Then add the brown and white sugar, baking powder and salt to the mixture and whisk until the sugar is dissolved and everything is well combined.
Now pour this batter into the fermented milk and flour. Use a whisk or metal spoon to combine the two batters. It can seem like they won't combine, but keep going, they will! The batter will be quite stretchy and feel different to a normal muffin batter.
Once the muffin batter is fully combined, carefully fold in the blueberries. You can use fresh or frozen (see notes below).
Now spoon the batter into your muffin tin. I choose not to use cupcake wrappers as I love the crispy outer you get without them.
Bake the muffins at 180C / 350F for approximately 20 minutes or until the tops are golden brown.