In a large bowl combine your flour, sugar, baking powder, baking soda, and salt.
Cut in your butter into the flour mixture with a pastry cutter, until your butter is the size of oats
Add your buttermilk and thyme and stir with a wooden spoon.
Flour your surface and then press out your dough into a rectangle about ¼ inch thick. Then tri-fold your dough into itself (like a trifold pamphlet). Press your dough out again to about ¼ inch thick. Then repeat your tri-fold. Slightly press your dough out again but this time keeping it to about 1 inch thick.
Using a biscuit cutter, cut out your biscuits. Then re-knead your scraps and repeat the above step. Then cut out the remaining biscuits. You should get between 4 and 6 total.
Mix your egg and ¼ cup buttermilk together and use it as a wash on the top of your biscuits.
Let your biscuits rest 15 minutes in the fridge. Pre-Heat the oven to 400 degrees F.
Bake biscuits for 15 minutes.
Serve immediately out of the oven!