Add softened butter to a large mixing bowl with the brown sugar. Mix with an electric hand mixer or paddle attachment of a stand mixer until light and fluffy.
Add the egg and vanilla extract to the bowl and mix again.
In a separate bowl combine all purpose flour, oats and baking soda. Mix together and pour dry ingredients into the bowl with the wet ingredients. Mix again with the mixer until evenly combined.
Fold chocolate chips into the batter with a flat spatula.
Cover dough and place in the fridge to chill for at least 1 hour.
Preheat oven to 350F and line 2 baking sheets with parchment paper.
Use a 2 tbsp cookie scoop to scoop dough balls onto lined baking sheets top with more chocolate chips if desired. Leave space between each dough ball.
Bake at 350F for 13 -15 minutes. Top with flakey sea salt if desired and cool on the sheet pan for a few minutes before transferring to a wire rack to cool completely.
** Bake from Frozen: roll into dough balls and freeze in balls. Bake directly from frozen at 325F for 17-18 minutes.
Notes
Use old fashioned rolled oats, not quick oats. Quick oats absorb moisture too fast and make the cookies soft and mushy instead of chewy. Old fashioned oats give you the best texture.
Do not overbake. Pull the cookies out when the edges look set but the centers still look a little underdone. They will firm up as they cool on the pan. Overbaked oatmeal cookies get hard and dry.
Measure your flour correctly. Spoon the flour into the measuring cup and level it off with a knife. Scooping directly from the bag packs in too much flour and makes the cookies dry and cakey.
Chill the dough before baking. Even 30 minutes in the fridge helps the cookies hold their shape and makes them chewier. If you have time, chilling overnight gives the best results.