1. Place the flour, baking soda, cream of tartar and sugar into the bowl of a food processor. Process briefly to combine.
2. Add the chilled Plugrá Butter and process off and on until the Plugrá Butter is finely cut into the dry ingredients.
3. Turn the mixture out into a large bowl and gradually add the chilled cream, cutting through the mixture with a large fork to combine. Do not stir the dough, or your biscuits will be tough.
4. Add enough half and half to make a soft dough. You may need a little more or a little less than 2 cups, depending on how dry your flour is.
5. Turn the dough out onto a floured surface and gently knead the dough five or six times. Being sure the surface is dusted with flour, roll the dough 1/2 inch thick. Use a 3-inch cutter to make the biscuits.
6. Place them on an unlined baking pan. If you would like the surface to have a sparkled effect, lightly brush the tops of the biscuits with just a bit of half and half, and sprinkle some sugar on them. Otherwise, bake them plain. (They will rise a bit more if you do not brush and sprinkle them.)
7. Immediately bake the biscuits on the middle rack of a 500 ºF preheated oven for 9-12 minutes, until golden brown.
8. Remove from the oven and let cool.