Preheat the oven to 425. Line two baking sheets with parchment paper.
Using a stand mixer fitted with a paddle attachment, combine the flour, baking powder, salt and baking soda and mix briefly on low speed just to combine. Add the chilled butter and continue mixing on low speed until the butter is cut into pea-sized pieces. Drizzle in the buttermilk and mix just until the dough forms a ball. Divide the dough into thirds.
In a small bowl, combine the cheddar, bacon and green onions. On a lightly floured surface and with a lightly floured rolling pin, roll out one piece of dough to an 11-by-8 1/2 -in/28-by-21.5 cm rectangle and layer on top of the dough with the cheddar mixture. Sprinkle the second layer of dough with the remaining half of the cheddar mixture. Roll out the remaining piece of dough and layer it on top. Gently roll out the dough layers to make a 12-by-10-in/30.5-by-25-cm rectangle.
Using a 2-in/3-cm biscuit cutter, stamp out 18 biscuits and put them on the prepared baking sheets. Brush the tops with cream. Bake until just starting to turn golden but before the bottoms begin to brown, about 15 minutes. Let cool slightly and serve warm.
(To make ahead, store in an airtight container at room temperature for up to 1 day in a toaster oven).
Make sure your ingredients are cold. Your butter and buttermilk must be cold and if your dough warms up, put it in the refrigerator for a few minutes to ensure flaky biscuits.