Preheat the oven to 350℉. Prepare cookie sheet(s) by lining each with a piece of parchment paper. Set aside.
In the bowl of a stand mixer fixed with the paddle attachment, cream together the butter, dark brown sugar, and granulated sugar until light and fluffy, about 3 minutes. Scrape down the sides of the bowl periodically to ensure even mixing. Add each egg one at a time, then add the vanilla extract.
In a separate mixing bowl, whisk together the bread flour, baking soda, ground cinnamon, ground nutmeg, Dutch-processed cocoa powder, and sea salt. With the stand mixer running on medium-low speed, pour in half of the dry ingredients and wait until they are fully incorporated before adding the remainder.
Switch to the lowest speed setting and pour in the old-fashioned rolled oats, raisins, and chocolate chips until evenly distributed throughout the batter.
Using a tablespoon-sized cookie scoop, portion out and roll each dough ball until round and smooth. Aim for 45-50g of dough per cookie and arrange 2 inches apart on a cookie sheet. Bake for 11-13 minutes, or until the edges are golden brown.
Allow the cookies to sit on the baking sheet for another 3-5 minutes before transferring to a wire cooling rack. While the cookies are still on the tray, press more chocolate chips into each cookie. Garnish with some fleur de sel, if desired.
