Brown your butter: melt butter in a saucepan over medium heat. The butter will begin to foam. Make sure you whisk constantly during this process. After a couple of minutes, the butter will begin to brown on the bottom of the saucepan. Continue to whisk and remove from heat as soon as the butter begins to brown and give off a nutty aroma. Transfer to a bowl to cool for 5-10 minutes, or until cool enough to touch.
Add every last bit of the brown butter, brown sugar and pure maple syrup to the bowl of an electric mixer, beat until smooth and well combined. Next add in the egg and vanilla and mix again until smooth, creamy and well combined. It’s very important to make sure your egg is at room temperature (you can do so by running warm water over the egg for 1 min).
In a large bowl, whisk together the flour, oats, baking soda, cinnamon and salt. Slowly add dry ingredients to the wet ingredients and mix on low-speed just until combined. Next, add in chopped pecans and mix on low speed until combined. Chill dough in fridge for about 30-60 minutes.
Once ready to bake, preheat the oven to 350 degrees F and line a baking sheet with parchment paper. Use a medium cookie scoop or your hands to grab a large heaping tablespoon full of dough. Roll into balls and place on the prepared cookie sheet, leaving at least 2 inches of space between each cookie.
Bake cookies 9-12 minutes. If you like cookies with a crispy edges, bake for about 12 minutes. If you like softer cookies, bake for 9-10 minutes.
Remove from oven and cool the cookies on sheets about 5 minutes then transfer to a wire rack. Repeat with remaining dough. Makes about 18 cookies.
Once cookies have cooled you can make the icing: add powdered sugar, maple syrup, melted butter, milk and salt to a bowl. Mix to combine. Icing should be smooth and spoonable. Spoon 2 teaspoonfuls of icing onto each cookie and spread out a little. Return to wire rack to let the icing harden.