Preheat the oven to 375F and line 2 baking sheets with parchment paper or silpat liners.
Cream together the butter and shortening in a large bowl. Cream in the sugar, then stir in the eggs and vanilla. In a separate bowl, whisk together the flour, cinnamon, baking soda, and salt. Gradually stir the dry ingredients into the wet, then mix in the oats, butterscotch chips, and walnuts.
Chill the dough until stiff but not completely hard, about 10 to 15 minutes in the freezer.
Scoop the dough onto the prepared sheets, leaving about 2 to 3 inches between each cookie (I use a 1 1/2 tablespoon measure to scoop out the dough).
Bake until the cookies are light golden brown on the edges and look ever so slightly doughy in the center, about 10 to 12 minutes, rotating the trays once halfway through cooking.
Cool for 5 to 10 minutes, on the tray, then transfer to a parchment paper-lined surface to finish cooling.