Preheat the oven to 180ºC/160ºfan. Grease and line a 9inch x 9inch cake tin.
In a mixing bowl, cream together the butter and sugar. Use a fork to break up the sugar if it's lumpy before adding to the butter.
Stir in the eggs and vanilla.
Sieve in the flour, salt and bicarb and stir together.
Add the milk and stir together.
Leave a handful of blueberries for the topping. Stir the rest into the mix.
Spoon the cookie dough into the pan and level out.
Stud the last blueberries on top.
Place in the oven and bake until golden brown. If you like your cookies slightly gooey take them out at 20 minutes. 20-25 minutes if you want them to be set more. Both work really well.
Serve and enjoy.