Preheat the oven to 400 degrees F and line a baking sheet with parchment paper.
Cut 1 1/4 cups (2 1/2 sticks) cold butter into small cubes.
Sift together the flour, baking powder and baking soda in the bowl of a stand mixer fitted with the beater attachment. Turn the machine on low and pour in the sugar, salt and yeast. Mix the dry ingredients together thoroughly. With the machine running, gradually add the cubed butter piece by piece. Allow the mixer to slowly cut the butter into the flour mixture until it resembles cornmeal with some pea-sized clumps, about 5 minutes. Add the fresh thyme leaves and mix for 30 seconds more to combine. With the machine still running on low speed, pour in the buttermilk and sour cream. This will pull the mixture together into a sticky dough. Turn the machine off and add the Cheddar. Fold the cheese into the dough on low speed, for about 30 seconds. Scrape the dough out onto a lightly floured surface. Pull the dough together into a smooth disc.
Using a floured rolling pin, roll the dough out until it is 1 inch thick. Use a floured 2-inch round biscuit cutter to cut out biscuits. Place the biscuits on the parchment-lined baking sheet. Collect the dough scraps and roll out and cut again just once more, then discard scraps.
Melt the remaining 1/4 cup (1/2 stick) butter in the microwave. Brush the tops of the raw biscuits with half of the melted butter.
Bake the biscuits until evenly golden brown, 22 to 25 minutes. Brush the biscuits with the remaining melted butter. Serve warm with sorghum, honey and marmalade.