Preheat oven to 450 degrees, and line a baking sheet with parchment paper.
Cut the 1/2 cup butter into very small chunks. Put in small bowl and place back into the fridge or freezer until ready to use.
In a large mixing bowl combine the sugar, flour, baking powder, cream of tartar, and salt.
Add the butter into the flour mixture. Using a pastry cutter, cut the butter into the flour mixture until you have pea sized butter throughout your biscuit dough.
Then add in the buttermilk and egg. Work it into the mixture just until barely blended. It will be sticky.
Place the dough on a floured surface. We found that the kitchen counter works great. Knead the dough about 5 to 10 times. Add a small amount of flour if the dough is too sticky. But don't overdo it.
Pat the dough into a rectangle about 3/4 of an inch thick. Fold it into thirds.
Gently roll dough into a rectangle again and fold into thirds. Repeat a third time. This will give the biscuits lots of light and fluffy layers.
Then roll the dough out into 1/2 - 3/4 inch thickness. Cut the biscuits using the biscuit cutter. We used a 3 inch diameter cutter. Be sure to push straight down and then straight up. No twisting.
Try to cut as many biscuits as you can, cutting them close together. Piece together the extra dough to make more biscuits.
Place biscuits on the prepared baking sheet. Gently brush biscuits with extra buttermilk. Dip the pastry brush into the buttermilk carton and you'll have enough to spread lightly over each biscuit.
Bake for 12-15 minutes or until golden brown on top. Remove from oven and baste with 1 Tablespoon melted butter.
Serve with butter and jam.