Preheat oven to 400°F/200°C
In a large bowl, whisk together the flour, sugar, baking soda, baking powder, and salt
Stir in the cooled, melted butter, buttermilk, heavy cream, and egg until a soft dough forms
Fold in the raisins if using
Divide the dough evenly into an extra-large silicone muffin tin, filling each cavity about ¾ full
Whisk together the egg yolk and milk and brush the tops generously
Bake for 25-30 minutes, or until the tops are golden brown and a tester inserted in the center comes out clean
Let cool slightly, then serve warm with butter, jam, and a sprinkle of flaky salt
