Preheat the oven to 350°F. Line 2 baking sheets with parchment paper.
Beat together the butter, brown sugar, and vanilla until fluffy, about 3 minutes. Mix in the egg and molasses. Add the flour, baking soda, salt, cinnamon, ginger, cardamom, nutmeg, allspice, and pepper. Mix until combined.
Mix the cinnamon and sugar in a small bowl.
Roll the dough into tablespoon-size balls, then coat each ball in cinnamon sugar. If the dough is sticky, add 1–2 tablespoons of flour. Place on the prepared baking sheets, 2 inches apart.
Bake for 8–10 minutes, until the edges are just setting but the centers are still soft. Don't overbake! Let cool on the baking sheets.
To make the icing, brown the butter in a small saucepan over medium heat until golden and nutty, 3–5 minutes. Let cool for 5 minutes, then whisk in the powdered sugar and milk until smooth and spreadable.
Spread the icing over the cooled cookies while they're still warm. Mix the vanilla bean powder, flaky salt, and cinnamon. Sprinkle over each cookie before the icing sets. Let the icing set, then enjoy!