Preheat the oven to 350 degrees and line two baking sheets with parchment paper. (The parchment paper does not need to be greased.)
In the mixer fitted with the paddle attachment, whip together the butter and shortening until smooth. Next, add in the sugar and brown sugar and mix until fluffy.
Add in both of the eggs, vanilla, salt, and cinnamon, mix until combined.
Next add the flour, baking soda, mix until combined.
Add in the 3 cups of oatmeal and the cup of butterscotch chips. Mix until just combined.
Scoop out about 2 tbsp of dough for each cookie and place on the lined baking sheet leaving 1" of space between them. Repeat until all the dough is gone.
Bake one sheet at a time on the center rack of the oven for 12-14 minutes. The edges of the cookie should be golden brown and the center should have risen when they are ready to come out of the oven. For a crunchier cookie leave in longer, for a softer cookie remover sooner.
Allow the cookies to cool for around 5 minutes before removing them from the baking sheet and placing them on a cooling rack to finish cooling.
Enjoy right away!