Preheat oven to 425 degrees F. Line a baking sheet with parchment paper.
In a large mixing bowl, combine flour, sugar, baking powder, salt, and cream of tartar; cut in cold butter until crumbly.
In a separate bowl, whisk together egg yolk and half & half; pour into dry mixture. Add mashed banana and Biscoff spread. Use your hand to combine just until incorporated. DO NOT OVERMIX or dough will be tough.
Turn dough out onto a floured surface. Pat into a large circle that is about 1 1/2 - 2 inches thick. Cut into 8 wedges. Place on prepared pan. Make an egg wash with the egg white. Brush tops of scones. Sprinkle with sugar if desired.
Bake for 15-18 minutes until a golden brown. If desired, make a glaze icing to drizzle on tops.