Preheat your oven to 425°F and butter a large muffin or cupcake tin. In a large bowl, whisk together the flour, sugar, baking soda, baking powder, and salt. Set aside.
In a separate medium bowl, whisk together the melted and cooled butter, buttermilk, heavy cream, and egg (do not use the ingredients listed for the egg wash here, just the scone dough).
Make a well in the center of your dry ingredients by pushing the dry ingredients away from the center. Add the whisked liquid ingredients into the middle of the well and stir with a nonstick spatula or wooden spoon to form a thick dough. It will be thick; you may have to knead it a bit with your hands to make sure there are no dry spots. If the dough does feel dry, drizzle in just a bit more buttermilk and mix again. If using raisins, add them now.
Using a cookie scoop, scoop heaping mounds of the dough into the greased muffin tin. In a small bowl, mix the egg yolk and heavy cream to create the egg wash. Using a pastry brush, gently brush the tops of the raw scone dough with the wash.
Bake for 20–25 minutes, until the tops are golden brown and a toothpick or knife inserted into the center comes out clean. If you find temperature helpful, use an instant-read thermometer to check if the inside of the scone is cooked; it should read 185°F.
Remove from the oven and serve warm with lots of jam, butter, and flaky salt.
