Place the strawberries in a large bowl, cover with white sugar and gently toss until all of the berries are coated. Cover the bowl and place in the fridge to allow juices and sugar to create a nice syrup on the bottom (about 30 minutes - 2 hours). Preheat oven to 350º F. Fill the bottom of a shallow dish with buttermilk. Open package of buttermilk biscuits, separate and dip each one (top and bottom) in the buttermilk before spacing them out on a baking sheet (use parchment/baking paper on the sheet for ease of removal). Sprinkle turbinado sugar on the both top and bottom of each biscuit. Place in oven and bake for about 16-18 minutes. Remove the biscuits from oven and let cool. When cool, slice each biscuit into two halves. Place the bottom halves on serving plates and spoon on the strawberries and syrup. Sprinkle on blueberries, too, if desired. Pour more of the strawberry syrup over the berries and biscuits if desired. Add a dollop of mascarpone atop the berries, and then gently set the top half of the biscuits over the berries like a "hat."