Preparation

Make the biscuits:

• Set a rack in the center of the oven; heat to 400°F. Line a baking sheet with parchment or lightly grease it with shortening or cooking spray. In a large bowl, whisk the flour, baking powder, salt, sugar, lemon zest, and nutmeg. With a pastry blender or your fingertips, cut in the butter until the mixture resembles coarse meal. Gently stir in the buttermilk until the dough just holds together with no large, dry lumps.  Spoon the dough onto the baking sheet in six equal mounds. Brush the tops with buttermilk; sprinkle with sugar. Bake until the peaks have begun to brown and the bottoms are golden, 20 to 25 minutes. Let rest for 1 minute and then transfer to a wire rack. While still slightly warm, slice them open with a serrated knife.

Make the blueberry filling:

• Set aside 2 cups of the berries. In a medium, nonreactive saucepan, combine the remaining 4 cups of blueberries, sugar, water, lemon zest, and nutmeg (if using). Cook, uncovered, over medium heat, stirring frequently until very soft and juicy, 6 to 7 minutes. Remove from the heat. Taste and add lemon juice and more sugar, if necessary. If not using immediately, cover and refrigerate. When ready to serve, reheat the blueberry sauce until very warm and stir in the reserved blueberries.

Whip the cream and assemble the shortcakes:

• Chill a mixing bowl and beaters for 30 minutes. In the bowl, combine the heavy cream, sugar, and vanilla. Whip until medium peaks form and the beaters leave tracks on top of the cream.
• Put the bottom half of each biscuit on a plate. Spoon on about 1/2 cup of the blueberry mixture and a few dollops of cream. Cover with the biscuit top. Spoon on more blueberries and top with another dollop of whipped cream. Serve immediately, passing any remaining blueberry mixture at the table.