In a mixing bowl combine flour, sugar, baking powder, bicarbonate of soda, and salt. Whisk together to remove any lumps and set aside.
In another mixing bowl combine the remaining ingredients except for the blueberries and whisk together.
Stir the wet mixture into the dry mixture and stir together. Gently fold in the blueberries until just combined (batter should be thick)
Scoop mixture into a piping bag or a re-closeable plastic bag and snip the tip. Pipe mixture into prepared doughnut moulds and bake for 22-25 minutes or until slightly darker than golden brown on top and doughnuts have begun to brown on the bottoms.
Remove from oven and allow doughnuts to sit for 5 minutes. Remove from moulds and place onto a cooling rack.
For the glaze: Place blueberries into a food processor and puree until smooth. Add the orange juice and icing sugar, ½ cup at a time) until fully incorporated and no lumps remain (the glaze should be very thin).
To assemble: Fully dip each doughnut into the glaze and shake to remove any excess. Allow glazed doughnuts to sit on a cooling rack for 5-10 minutes before serving (doughnuts should still be sticky after glazed; the glaze should stay wet).
If you do not wish to glaze the doughnuts you can simply sprinkle with icing sugar.