This is an American recipe, 'biscuits' being much more like savoury scones than cookie-style biscuits as we know them in Australia. They are delicious served as an accompaniment at meal times, especially when you need something to mop up gravy or sauce.
1/4 teaspoon (generous) salt
These biscuits are best eaten warm from the oven, but they can be made up to 1 day ahead, cooled and stored airtight at room temperature. To rewarm them, wrap the biscuits in foil and bake them at 350°F for about 10 minutes, or until they are heated through.
Position a rack in the center of the oven and preheat the oven to 425°F.
Onto a sheet of wax paper, sift together the flour, sugar, baking powder, salt, and baking soda, then sift the flour mixture again into a bowl. Using your fingertips, blend in the butter until the mixture resembles a coarse meal. Add the buttermilk and stir with a fork until the mixture is moistened (do not over mix the dough).
Turn the dough out onto a floured surface and knead gently just until the dough holds together loosely. Pat out the dough on the floured surface to about an 8x5-inch rectangle. Using a 2 1/2-inch-diameter biscuit cutter, cut out the biscuits, flouring the cutter between each cut. Transfer the biscuits to a heavy large baking sheet, arranging the biscuits about 2 inches apart. Brush the tops of the biscuits with milk or cream.
Bake for about 15 minutes, or until the biscuits are puffed and pale golden. Serve warm.