In a large bowl, mix together the flour, salt, baking powder, sugar, and baking soda.

Add the cold and diced butter. Use a pastry blender to cut in the cubed butter until the mixture is blended to resemble sand with tiny pebbles.

Pour over the buttermilk. Use your hands on a wooden spoon to create a shaggy dough.

Turn that dough onto a lightly floured surface. Knead it to bring it together into a cohesive, smooth dough.

Roll into a rectangle of 12 x 9 inches.

Sprinkle the grated butter all over that rectangle. Then fold the dough into a letter by bringing the bottom 3rd up to the middle and the top part over that. Then roll that into a rectangle to secure the butter. (*Approximately 9 x 12 inches in size)

Dust lightly with flour. Give the dough a 90 degree turn. Repeat this folding and rolling process 4 more times.

Then roll into a final rectangle, approx. 8 x 12 in size.

Cut biscuits by cutting out 9 equal rectangles. OR dip a biscuit cutter in flour and stamp out biscuits. If using a biscuit cutter, do not turn the cutter while cutting the biscuits. Stamp down hard and pull up. Repeat with remaining dough.

Place onto parchment lined baking sheet. Chill in freezer for 15 minutes.

Then beat water with egg for egg wash. Brush biscuits with egg wash and sprinkle with flaky sea salt. Bake 15-20 minutes, or until biscuits are golden brown and well risen.