How to Make It
Preheat oven to 450°F. Line a baking sheet with parchment paper.
Make the scones: Place flour, sugar, baking powder, salt, and baking soda in a food processor and pulse to combine. Add butter and pulse until sandy. Transfer to a large bowl; stir in nuts and white chocolate chips.
Make a well in dry ingredients and gradually add milk, using a fork to stir into a shaggy dough. Turn onto a lightly floured surface and gently knead until no dry spots remain.
Roll dough to an 8-by-10 inch rectangle, about ¾ inch thick; cut into 12 squares and transfer to prepared sheet. Bake until golden, 12 to 15 minutes, rotating halfway through.
Make the glaze: Melt butter in a medium pot over medium. Add sugar and cook, stirring, until sugar is melted and smooth. Remove from heat and add milk (mixture will bubble and seize). Bring to a boil, reduce heat to medium, and cook, stirring, until smooth and caramel colored, 8 to 10 minutes. Stir in kosher salt.
Spoon 1 tablespoon glaze over each scone. Top with nuts and flaky salt, if using.