Chocolate Salt & Pepper Sable Cookies

all purpose flour

dutch-process cocoa powder, sifted

instant espresso powder (optional)

baking soda

kosher salt

salted European-style butter* such as Kerrygold, at room temperature

packed light brown sugar

granulated sugar

egg yolk

dark chocolate (60-70%), grated or very finely chopped in a food processor

dark chocolate, chopped, for dipping/drizzling

large flake sea salt (such as Maldon) and fresh coarse ground black pepper