*TIP: Cut up your butter and put it in the freezer for about 10 minutes before you start anything else. It is much easier to cut the butter into the dry ingredients and it makes a better crumb.
Preheat your oven to 400F / 200C.
Combine flour, baking powder, sugar, salt, and cream of tartar. Cut in butter until fine crumbs.
In another bowl, beat egg slightly. Add milk and vanilla extract. Mix into flour to form dough. Gather the dough into a ball and knead lightly on a floured surface - just enough (4 times) so the dough has a smooth surface.
Gently work in your "variation". (I used frozen blueberries my first time.) Shape the dough into a circle about 1/2 inch thick. Cut it into wedges and put it on a baking sheet.
Bake at 400F / 200C for 10 minutes. If you're making the apple variation, cut your temperature to 350F / 160C and add more time.
Make your glaze: Stir your powdered sugar with a touch of milk and flavoring of your choice. Be careful as you add the liquid as the sugar becomes liquid fast. Mix it to your desired consistency.
When the scones come out of the oven, let them cool a little and then drizzle the glaze over the tops.