In a large mixing bowl, combine the melted butter, brown sugar, granulated sugar, and molasses. Use a silicone spatula to mix together. Add the egg, extra egg yolk, and vanilla and mix well.
Add the flour, oats, baking soda, ginger, cinnamon, cloves and salt and fold until just combined and no streaks of flour remain. The dough will seem wet–don’t worry this is right! Allow the dough to rest for 10 minutes while you preheat the oven. The flour and oats will absorb some of the wet ingredients and the dough will thicken before your eyes!
Preheat the oven to 350°F and line two cookie sheets with parchment paper. Use a 1 ½ ounce cookie scoop to portion out equal amounts of dough. Place on the prepared baking sheets, spacing the dough 2 inches apart.
Bake until the cookies have puffed up and are light golden brown around the edges but still somewhat soft in the middle, 9 to 10 minutes. Let the cookies sit on the baking sheet for a few minutes to firm up slightly before icing.
While the cookies are baking, make the icing. Combine the powdered sugar, milk, vanilla and salt in a small bowl and whisk until smooth. Spoon the icing over the warm cookies (this will help the icing to harden!), spreading it to the edges. Leave the cookies on the baking sheet until the icing is fully set and the cookies are cool. Devour!
Notes
We like to use dark molasses in these because it has a deep, rich flavor. Blackstrap molasses will have a more intense, bitter flavor!