In a large mixing bowl, whisk together the oats, all-purpose flour, baking powder, baking soda, and spices—ground ginger, cinnamon, nutmeg, and cloves.

In a separate bowl, beat the room temperature butter with brown sugar and granulated sugar until light and fluffy, then add the molasses, egg, and vanilla extract, mixing until fully incorporated.

Gradually add the dry mixture to the wet ingredients, mixing on low speed just until combined.

Cover the dough and chill in the refrigerator for at least 30 minutes.

Preheat your oven to 350°F (175°C) and prepare baking sheets by lining them with parchment paper.

Remove the dough from the fridge and portion it onto the prepared baking sheets.

Bake for 13-15 minutes, or until the edges are golden brown.

Allow to cool on sheets for 5 minutes before transferring to wire racks.

Prepare icing by whisking together powdered sugar, milk, and spices until smooth, then ice the cookies.