1) Whisk together the flour, cornstarch, salt, baking powder, and sugar. Stir in enough heavy cream to moisten the dough thoroughly. You'll probably use about 1 cup in the summer, 1 1/4 cups in the winter, and 1 cup + 2 tablespoons at the turn of the seasons. You want to be able to gather the dough together, squeeze it, and have it hang together easily, without dry bits falling off.
2) Turn the dough out onto a lightly floured work surface, and very gently pat it into an 8" circle about 3/4" thick. If you're uncertain about your ability to make a nice freeform 8" round, pat the dough into a lightly floured 8" round cake pan, then turn it out onto a lightly floured surface.
3) Use a sharp 2 ¼" biscuit cutter to cut rounds. Place them on a lightly greased (or parchment-lined) baking sheet.
4) Brush the biscuits with butter, if desired, for extra flavor.
5) Place the pan in the freezer for 30 minutes. This will improve the biscuits' texture and rise.
6) Preheat the oven to 425°F while the biscuits are in the freezer.
7) Bake the biscuits for 20 minutes, till they're golden brown. Remove from the oven. If you have any melted butter left over, brush it on the baked biscuits. Serve immediately.