In the bowl of a stand mixer fitted with paddle attachment, or in a large bowl using an electric hand mixer, cream butter and brown sugar on medium speed until well combined (2 to 3 minutes). Scrape down sides of the bowl. Reduce speed to low, add egg and rum extract. Bring speed back to medium and mix until consistency is fluffly (3 to 4 minutes).
In a separate bowl, whisk together flour, cinnamon, baking soda and salt. Set aside.
With mixer on low speed add in coconut flakes and quick oats until combined. Then add combined dry ingredients a quarter cup at a time to butter mixture until just combined (don't over mix). Scrape down bowl with a spatula as needed. The dough should be thick
Remove dough from bowl and cover tightly with plastic wrap. Refrigerate for 1h (or 30 minutes in the freezer). If thinner cookies are preferred, skip this step.
Preheat oven to 350°F (or 177°C). Line 2 baking sheets with silicone baking mats or parchment paper (cut paper to fit trays perfectly instead of leaving an overhang).
Remove dough from refrigerator and scoop dough with a small cookie scoop or 1/8 measuring cup, (See *Notes* on cookie size and chewy texture). Roll and shape scooped dough into round ball with your hands. Place dough ball on tray and press lightly with index finger to flatten the top. Space each cookie ball 2 inches apart to leave room for the cookie to spread during baking.
Bake 1 tray at a time (on middle oven rack) for 10 minutes until cookies are lightly brown (note that oven temperature may vary, adjust bake time accordingly by 2 or 3 minutes more). Do not bake for more than 13 minutes if chewy texture is desired. Immediately flatten cookie with the back of a drinking glass or soup spoon.
Let cookies cool on tray for 5 minutes, then transfer to a wire rack with a flat spatula to cool completely.