Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper or silicone baking mats to prevent sticking and promote even baking.

In a medium bowl, add the old fashioned rolled oats. Pour in 1/4 cup of warm water and stir briefly. Let the oats sit and soften while you prepare the rest of the dough. This helps create a softer, chewier texture while keeping some oat flecks.

In another medium bowl, whisk together the all-purpose flour, baking soda, baking powder, ground cinnamon, ground nutmeg, and fine sea salt until the spices are evenly distributed.

In a large mixing bowl, beat the softened butter, light brown sugar, and granulated sugar together with a hand mixer on medium speed for 2–3 minutes, until light and fluffy. If mixing by hand, use a sturdy spoon and beat well until creamy.

Beat in the eggs one at a time, mixing well after each addition. Add the vanilla extract and mix until fully combined and the batter is smooth.

Add the softened oats (including any remaining water) to the butter mixture and mix on low speed just until combined. Add the dry ingredient mixture in two additions, mixing on low only until no visible streaks of flour remain. Scrape down the sides and bottom of the bowl as needed.

If using raisins, chopped nuts, or mini chocolate chips, fold up to 1 cup total into the dough with a spatula. The dough will be thick and slightly sticky.

Using a 1 1/2-tablespoon cookie scoop or a rounded tablespoon, portion the dough onto the prepared baking sheets, leaving about 2 inches between cookies. Lightly flatten the tops with your fingers or the back of a spoon to encourage even spreading.

Bake each sheet for 10–12 minutes, or until the edges are set and lightly golden while the centers still look slightly soft. Cookies will continue to firm up on the hot pan after baking, so avoid overbaking.

Let the cookies cool on the baking sheet for 5 minutes, then transfer them carefully to a wire rack to cool completely. Make sure they are fully cooled before icing so the glaze does not melt off.

In a medium bowl, whisk together the powdered sugar, 2 tablespoons of milk, vanilla extract, and a pinch of salt until smooth. The glaze should be thick but pourable, similar to slightly warmed honey. If too thick, add milk 1/2 teaspoon at a time; if too thin, whisk in more powdered sugar.

Once the cookies are completely cool, drizzle the icing over the tops with a spoon in zigzags, or dip the top of each cookie lightly into the glaze. Let excess drip off, then place the cookies back on the wire rack.

Allow the iced cookies to sit at room temperature for 30–45 minutes, or until the icing is dry to the touch and lightly crackled. Once fully set, the cookies can be stacked or packed for storage or gifting.