In a mixing bowl, combine the flour, baking powder, salt and sugar.
Grate the frozen butter into the bowl and using your fingertips, rub it into the mixture until it resembles coarse breadcrumbs with some bigger bits of butter scattered throughout.
Stir in the berries gently and then pour in the cream. Bring the dough together with a silicone spatula, then use your hands to shape it into a rough mass. Don't overwork the dough or you'll end up with tough scones. It's ok if the blueberry juices start to leak a bit, but try not to burst the berries. If you need to, add an extra tablespoon of cream if the dough feels too dry.
Tip the dough out onto silicone baking mat and pat into an 8" wide circle. Slice into 8 equal triangles with a sharp knife. If this step is getting messy because of the berries, slide the mat onto a baking tray and place it in the fridge before shaping and slicing.
Once sliced, chill the dough for 20 minutes.
Preheat the oven to 200 C.
Now separate the sliced dough, placing each scone at least an inch apart on the baking tray. Mix the cream and water in a small bowl, then brush over the top and sides of each scone.
Bake for 25 minutes or until golden-brown on top and puffy. Let them cool completely before glazing.
To make the glaze, combine the sugar and lemon juice, stirring into a smooth glaze. Add the water if you need to thin it out a bit then drizzle over the scones immediately. The glaze will set and harden in about 15 minutes.
Scones taste best on day one in terms of texture, but can be stored at room temperature 2 to 3 days in an airtight tin, and in more humid areas, they are best stored in the fridge after day one, where they will keep for a week. Remember that when they're stored in a closed box, the crips tops will soften, but this doesn't affect the flavour. Happy baking!