In a saucepan, melt the butter over medium heat. Whisk butter occasionally until the butter begins to brown and it develops a nutty aroma. Transfer butter to heatproof bowl and let cool for about 30 minutes. (Be careful not to burn the butter, remove from stovetop just as it starts to brown.)
In a medium bowl, combine the flour, oats, salt, baking soda and spices. Set aside.
Setup a stand mixer with the paddle attachment. In the mixing bowl add both sugars, molasses and browned butter. Mix until well combined. Beat in the eggs and mix until smooth.
Add the flour mixture and mix until it is just combined. Do not over mix.
Prepare a baking sheet with parchment paper and scoop the dough out into portions. (use a cookie/ice cream scoop for even portions) Chill the dough balls in the refrigerator for at least 20 minutes. (At this stage you can also freeze the dough balls. Portion them onto the cookie sheet and set in freeze until firm and then transfer to a container. They will keep frozen for up to 3 months. Put cookies in fridge overnight to thaw the day before baking.)
Preheat oven to 350 degrees F. Line two cookie sheets with parchment paper. Place the chilled dough balls about 3 inches apart and bake for about 8 minutes. You want these cookies to be set on the outside and still look slightly gooey in the middle. They will continue to set as they cool.