Pre-heat the oven to 180°C (350ºF) and grease a 6" / 18cm cake tin (I used a springform).
Melt the butter and set to one side.
Mix the flour, baking powder, baking soda and sugar together in a bowl.
Beat the egg then whisk in the Greek yoghurt, oil, milk, lime and vanilla extract along with the cooled butter.
Pour into the dry ingredients and mix until just combined.
Stir in the blueberries (see notes for a tip to prevent them sinking).
Dollop into the prepared tin (the batter will be very thick).
Bake for around 25 minutes, just until the top is firm to the touch and an inserted skewer comes out clean.
Cool in the pan for ten minutes or so, then either turn out onto a wire rack, or remove the outside layer (if using a springform pan).
Allow to cool completely, sprinkle with a little icing sugar if you like, then slice and enjoy!