Preheat oven to 180°C (160°C fan) and line a 12-hole muffin tin with paper cases.
In a large bowl, combine the self-raising flour and caster sugar.
In a separate bowl, whisk together the eggs, milk, melted butter, and Honeyberry Lemon Extract until smooth.
Pour the wet mixture into the dry ingredients and stir gently until just combined (do not overmix or the muffins will be dense).
Gently fold in the freeze dried blueberries, reserving a few for sprinkling on top.
Divide the mixture evenly between the cases, top with reserved blueberries (and a sprinkle of demerara sugar if using), and bake for 18–20 minutes, until golden and springy to the touch.
Allow muffins to cool in the tin for 5 minutes before transferring to a wire rack. Best enjoyed slightly warm!