Preheat the oven to 400℉ (205℃).
In a large mixing bowl, whisk the flour, baking powder, baking soda, sugar, and salt.
Quickly grate frozen butter into the bowl of flour (grating butter ensures the fat distributes evenly for light and fluffy). Mix well until it resembles coarse crumbs. Or cut the butter into the flour mixture with a pastry blender until the mixture resembles coarse crumbs; this might take about 5 minutes.
Make a well in the center of the flour mixture, add the buttermilk, and stir with a spoon until it forms a rough ball—avoid overmixing. Let it rest in the fridge for about 10 minutes. That gives the butter a chance to firm back up.
Turn the dough out onto a floured surface and knead it 3-4 times, just enough for it to come together.
Gently pat or roll it out to about ½ inch thick. Then fold the dough onto itself in thirds, roll it out again, and repeat the folding process about 6 times to ensure flakiness. Go gently on the rolling process, and after the folding process is complete, roll the dough out to a 1-inch thick rectangle.
Use a 2-inch round cookie cutter or drinking glass to cut out the biscuits, and space them evenly on your prepared baking sheet. (My pictures show 9, but you can knead the scraps and roll them out to make the other 3 for a complete dozen. They're just not as pretty.)
Brush with cream, and bake at 400℉ (205℃) for 12-15 minutes or until lightly browned.
Remove and serve warm.