1. Preheat oven to 450°.
2. In a medium mixing bowl, sift together first 5 ingredients (through cream of tartar).
3. Using a food processor or pastry cutter, cut butter into dry ingredients until butter is in pea-size pieces; stir in mix-ins, if desired.
4. In a small dish, whisk egg with 2 tbsp. cream and vanilla, if using; pour egg mixture into dry ingredients.
5. Using a fork, stir remaining cream into dough a little at a time as needed until dough is uniformly moist and soft but not sticky (there will be lumps).
6. Move dough to a large sheet of waxed paper; using a second sheet of waxed paper (not your hands), pat dough into a rough square shape about 9" wide, taking care not overwork the dough (sprinkle a bit of flour on the waxed paper if dough is very sticky).
7. Brush dough with a little bit of cream to moisten; sprinkle with turbinado sugar.
8. Using a sharp knife or bench scraper, cut dough into 9 squares. Place 1 ½" apart on a parchment-lined baking sheet; bake in preheated oven until golden-brown (10-12 min.).
9. Remove from oven; transfer to a wire rack to cool.

Tasty Tip:

• For wedge-shaped scones, pat dough into a 9" circle and cut into 8 wedges. A biscuit cutter of any shape or size can also be used to shape your scones, rerolling scraps very lightly.