1. Preheat oven to 300 degrees F. Sift together the flour, salt, and baking powder; set aside. In a large bowl, use the paddle attachment of a mixer to beat together sugar and butter on medium speed until creamy. Add cream, eggs, sour cream, and cream cheese, mixing after each addition. Add flour mixture and blend on low speed for a few seconds until combined. Add blueberries and mix another few seconds until they are evenly distributed. Do not overmix.
2. Place the dough on a floured surface. Cover top of the dough generously with flour and roll to 3/4-inch thickness. Using a round 3-inch cookie cutter, cut out the scones and place them on a baking sheet lined with parchment paper. Combine the scraps, roll to 3/4-inch thickness, and cut more scones. Discard remaining dough, as it will be too tough from frequent handling to use. If desired, sprinkle brown sugar on top of scones before baking.
3. Bake for 30 to 35 minutes, or until the tops start to turn golden brown.