Whisk together the flour, baking powder, baking soda, salt, cinnamon, ginger, nutmeg, allspice, and cardamom. Stir in the oats. Set aside.

Using an electric mixer on medium speed, beat the butter and brown sugar until light and fluffy. Add the eggs, one at a time, mixing well after each addition. Mix in the vanilla.

Reduce mixer speed to low. Gradually add the flour mixture, mixing just until combined.

Refrigerate the dough for at least an hour.

Drop the dough by 2-tablespoon portions (I use a #30 scoop) onto the prepared pans. Slightly flatten the top of each cookie.

Bake 12 to 14 minutes, or until the edges of the cookies are browned.

Cool the cookies on the pan for 5 minutes. Then transfer the cookies to a wire rack to cool completely.

Combine the confectioners' sugar and 2 tablespoons of milk. Add more milk, about a teaspoonful at a time, until the glaze is still thick but pourable.

Top each cooled cookie with glaze. Set the iced cookies on waxed paper to allow the icing to set.