1. Preheat oven to 425. Line a baking sheet with parchment paper.
2. In a mixing bowl, add the flour, sugar, salt, baking powder, and cream of tartar, stirring to combine. In a smaller bowl, stir together the yogurt and milk. Add the yogurt to the flour mixture and stir gently until it all comes together and a soft dough forms, being careful not to overwork the dough.
3. Turn the dough out onto a floured surface and pat it lightly into a circle, about 1-inch thick. Using a biscuit cutter, cut rounds of the dough and place them onto a prepared baking sheet. Repeat until all the dough has been used.
4. Bake about 13-15 minutes or until cooked through and golden. Serve immediately, while hot. Great with butter and jam or honey, with gravy, or as the bread for a breakfast sandwich, etc.
Because of the absence of fat in this recipe, the biscuits do toughen up some as they cool. For that reason, they are best served fresh from the oven while still hot. Any leftovers can be stored in a bag or airtight container and rewarmed before serving.