Buttermilk Biscuits

1 1/2 cups unbleached flour
1 1/2 tsp baking powder
1/2 tsp baking soda
3/4 tsp salt
1/2 tsp sugar
1/3 cup cold butter
1/2 to 1/3 cup buttermilk

Sift together flour, baking powder, soda, salt and sugar in mixing bowl. Cut butter into the mixture with fork or pastry blender until it resembles coarse crumbs. Add 1/2 cup buttermilk and mix (it will be a bit crumbly). Turn out the mixture onto a lightly floured surface and knead 8 to 10 times (adding more buttermilk if necessary) until dough is smooth. Do not overknead. Cover with a damp towel and let sit 10 to 15 minutes (or wrap in plastic and refrigerate for later use) Pat dough into a 4x8-inch rectangle, 3/4 to 1-inch high. Cut into 2-inch squares or use a biscuit cutter. Place on ungreased sheet pan and bake for 15 minutes at 400 degrees. Serve warm with butter or jam.