To make Martha Stewart’s raspberry cobbler from fresh raspberries, preheat the oven to 375 degrees Fahrenheit. In a mixing bowl, combine 5 cups of raspberries, or about 1 pound 10 ounces, with 3/4 cup of granulated sugar, 2 tablespoons of cornstarch and 1/4 teaspoon of coarse salt. Transfer the berries to a 9-inch square baking dish that is at least 2 inches deep.
In a separate mixing bowl, combine 1 3/4 cups of all-purpose flour, 1 3/4 teaspoons of baking powder, 1/4 cup of granulated sugar and 1/4 teaspoon of salt. Using butter knives or a pastry cutter, work in 6 tablespoons of cold unsalted butter until the mixture has a crumbly texture, with the crumbles approximately the size of small peas. Stir in 3/4 cup of heavy cream with a fork until the cream is just incorporated.
Transfer the dough to a clean surface, and knead it a couple of times to work any looses pieces into the dough. Pat the dough down to about 1 1/4-inch thickness, and cut it into 9 roughly square pieces. Brush the pieces with heavy cream, and sprinkle them with sanding sugar.
Top the berries with the pieces of dough, and bake them together for approximately an hour, or until the berry mixture is bubbly and the biscuits are golden brown on top. Allow the cobbler to set for a minimum of 30 minutes before serving.