Preheat and prepare cookie sheets. Preheat oven to 350°F. Line a cookie sheet with parchment paper or silicone baking mat. (note: if chilling your dough, do not preheat your oven until ready to bake).
Whisk dry ingredients. In a medium sized mixing bowl whisk together flour, baking soda, salt, and cinnamon and set aside.
Cream butter and sugar. In a second mixing bowl with an electric mixer (I use my stand mixer with a paddle attachment) cream together the softened butter, brown sugar, and granulated white sugar on medium speed for about 2 minutes and light and creamy.
Add wet ingredients. Add in your eggs one at a time beating to combine after each addition. Then add in the vanilla extract, and molasses and beat to combine.
Add in your dry ingredients. Add the flour mixture to the butter mixture and stir to combine. Stir just until no flour streaks remain.
Stir in the oats. With a rubber spatula, stir in the quick oats. I prefer the texture of quick oats for these oatmeal cream pies, but If you don’t have quick oats simply use your food processor to break down old-fashioned oats into quick oats! (I like to chill my cookies for 24 hours before baking as it yields a softer cookie, but I've made this with and without chilling and both turn out great.)
Scoop the cookies. Using a 1-inch cookie scoop, or tablespoon scoop the cookies into 1 ½-inch balls onto prepared cookie sheets about 2 inches apart.
Bake and cool the cookies. Bake cookie sheet on the middle rack for 10-12 minutes, until lightly browned on the sides. The centers will look very soft. Remove from the oven and let cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely. Remove from the cookie sheet and allow to cool on a cooling rack.