Place stick of butter in the freezer. Preheat oven to 450°F. Grease a 8"x8" baking pan and set aside.
To a food processor, add flour, baking powder, baking soda, salt, thyme and shredded cheddar cheese. Pulse until well combined.
Chop very cold butter and add to the food processor. Pulse until the butter is pea-sized.
Next, add buttermilk to the food processor and pulse again until the dough just forms a ball.
Turn the dough out onto a hard surface that has been dusted with flour. Using your fingers, press the dough into a rectangle. Fold the dough over and press it out into another rectangle. Repeat folding and pressing five times.
Place the dough into a prepared baking dish and press the dough out so that it fills the pan. Using a knife or bench scraper, cut the dough into 9 equal squares (three slices on one side, three on the other).
Bake for 20 minutes. Remove the pan from the oven, cover it with foil and bake for another 20 minutes until the biscuits are golden brown and cooked through.
Baste the biscuits with one tablespoon of melted butter when they first come out of the oven. Serve while hot.