Set the oven rack to the center position—Preheat to 375ºF (191ºC).
Line two large baking sheets with parchment paper.
In a small bowl, whisk together flour, salt, and baking soda. Set it aside.
Heat butter in an 8-inch skillet over medium-high heat, swirling to melt evenly. Stir and cook, scraping the bottom of the pan with a spatula until butter is golden brown and nutty in aroma, 1 to 2 minutes.
Transfer browned butter to a large bowl, making sure to scrape all of the bits from the pan. Stir in cinnamon and nutmeg. Add brown sugar, granulated sugar, and oil. Whisk together until combined. Whisk in eggs, egg yolk, and vanilla until smooth.
Use a spatula to fold the flour mixture into the butter mixture until combined, 1 minute.
Stir in oats, chocolate chips, pecans (if using) until combined. The dough will be stiff in texture.
Divide the dough into ¼ cup (60g) sized portions. Roll into a ball and place 2-inches apart on the baking sheet, 8 cookies per pan.
Use the bottom of a measuring cup or ramekin to press each dough ball into 2 ½-inch wide cookies. Re-form edges into a circle if needed.
Bake one sheet at a time. The edges should be set, lightly browned on the surface, and the centers soft but not wet, about 8 to 10 minutes. Rotate halfway through baking.
Let the cookies sit for 5 minutes and then transfer to a wire rack. Cool completely before serving.
Cookie Dough Size: 2 ounces; 60g; ¼ cup packed.
Make it Gluten-Free: Substitute gluten-free flour for all-purpose flour, and make sure the rolled oats are certified gluten-free. I recommend Bob's Redmill 1:1 Gluten-Free Baking Flour.
For Extra Flavor: Sprinkle some flaky sea salt like Maldon’s, just a tiny amount on top of each cookie before baking. It enhances the cocoa flavor and balances the sweetness.
Storing: Place inside an airtight container for up to 7 days. Freeze for up to 2 months, bring to room temperature.