Preheat the oven to 425F

In a large bowl, whisk flour and sugar

Cut in the butter until the mixture is crumbly

Slowly add the buttermilk, stirring with a wooden spoon until it forms a loose dough

Turn the dough out on a lightly floured surface and form into a square about 1 inch thick

Cut into quarters, stack on top of each other, and roll out again

Roll into a square, cut, and stack once more

Finally, roll into a rectangle about 3/4 inch thick

Cut into about 15-20 pieces

Place the cut biscuits on a baking sheet and place in the freezer for 10 minutes (this makes them more fluffy)

Brush the tops of the biscuits with the egg and sprinkle with a small amount of salt

Bake for about 15 minutes, until golden brown

Serve warm with butter or jelly