Preheat the oven to 400 degrees
In a medium bowl, stir together the flour, sugar, salt, baking soda, and baking powder.
Dice the butter and add it to the flour mixture. Work the butter into the flour mixture until it's evenly distributed and smaller than peas. Use two knives, a pastry cutter, or your fingertips (quickly squeeze the butter pieces between your fingers pressing them into little flakes.
Whisk heavy cream, egg yolk and lemon zest in a small bowl. Pour ontothe flour mixture and stir until a shaggy dough forms. Don't overmix, but incorporate things well.
Scoop the dough out, place it on the baking sheet, and use the warmth of your hands to fold and press dough together until it sticks together into a round disc form.
Cut the dough circle into 4-6 even pieces. Brush each piece with extra heavy cream. (Cut by pressing knife in one downward motion, don't use a sawing motion which will cause uneven rising)
Bake for 13-15 minutes, until a toothpick inserted comes out clean and they lightly brown on the edges.
While the scones bake, whisk together the glaze ingredients.
Glaze the scones when cool.