In a medium-sized bowl whisk the sourdough discard, 1 large egg, vanilla, and 3 tablespoons of heavy cream. Set aside.
In a large mixing bowl whisk the flour, salt, sugar, and baking powder. Use a cheese grater to grate the frozen butter into the flour mixture. Mix the cold butter into the flour. Next, add in the blueberries with raspberry and give it a quick mix to coat the berries in the flour mixture
Pour the wet ingredients into the dry ingredients, and use a wooden spoon or a spatula to incorporate them together. Do not over-mix the scone batter. The more you mix it the tougher the dough will become. The dough should be crumbly and thick.
Dump the scone mixture on a clean countertop and shape the batter into an 8-inch circle. You can use a rolling pin to smooth out the top and make it even.
Using a bench scraper divide the circle into 8 even slices.
Line a baking sheet with parchment paper and gently transfer the scones to it. Use a bench scraper to transfer them.Place in the fridge for 30 minutes to cool down the butter once again, this step will help the scones to keep their shape while baking. Brush the top of the scones with heavy cream and sprinkle with coarse sugar. Preheat the oven to 400 F. Bake for 20 minutes.
While the scones are baking make the cream cheese glaze. In a small bowl whisk the cream cheese, 3 tablespoons of heavy cream, 2 tablespoons of powdered sugar, and lemon zest.
Remove the scones from the baking sheet and place them on a cooling rack, drizzle with cream cheese frosting. Serve warm.