Adjust oven racks to the upper middle and lower middle positions and preheat oven to 375 degrees. Line 2 baking sheets with parchment paper or silicone mats. In a medium bowl, combine flour, baking soda, salt and cinnamon.: When you preheat, you should smell a faint warmth after a few minutes, but no strong odors. A fully preheated oven ensures even rise and consistent browning across batches. If the oven is not fully hot, cookies can spread unevenly and bake too long, resulting in a dry interior. A common mistake is underestimating preheat time, so wait until the oven reaches the set temperature before baking.
In a stand mixer fit with the paddle attachment on medium speed, or with an electric mixer, beat together butter, white sugar, brown sugar, eggs, and vanilla extract.: The surface should feel dry and slightly textured under your parchment or mat. These liners prevent sticking and help the bottom of the cookies brown evenly without burning. Without liners, cookies can stick and break when you transfer them, so always prepare sheets ahead of time. A typical error is using a thin sheet that allows hot spots, so choose a heavy cookie sheet if possible.
Reduce speed to low and gradually add the flour mixture. By hand, stir in the oats and butterscotch chips until just combined (if you use an electric mixer, you may break the chips).: As you whisk these, you will notice the cinnamon scent rising, which signals even distribution of the spice. This dry mix ensures every bite gets balanced flavor and even leavening. If you skip sifting or mixing well, the cookies may have pockets of baking soda or uneven spice. Avoid large clumps in the flour by stirring thoroughly.
Working with 1 heaping tablespoon of dough at a time, roll dough into 1 1/2-inch balls and lay on prepared baking sheets about 2 inches apart. (I use the OXO medium cookie scoop, a size 40 portioner, and do 12 scoops of dough per baking sheet).: The bowl will become creamy and pale as air gets incorporated, and the sugar will start to dissolve into the butter. This creaming step traps tiny air pockets that improve texture and lightness. If the butter is too cold, it will not cream well, producing dense cookies. Common pitfalls include overbeating which can introduce too much air, leading to excessive spread.
Bake for 7 to 8 minutes for chewy cookies, or 9 to 10 minutes for crispy cookies. Cool on baking sheets for 2 minutes and transfer to wire racks to cool completely (if you don't let the cookies cool, they may crumble).: As you add the dry mix slowly, the dough will go from glossy to thicker and more cohesive, with a faint floury aroma subsiding. Gradual addition prevents pockets of dry flour and overworking the dough. If you add everything at once, you risk clumping and uneven hydration. Avoid mixing on high which can toughen the dough from excess gluten development.
By hand, stir in the oats and butterscotch chips until just combined (if you use an electric mixer, you may break the chips): You will feel the dough become studded and textured, and the sweet butterscotch pieces will glint through the mixture. Stirring by hand preserves the shape of the chips and keeps the oats intact for ideal chew. Overmixing can crush chips and mangle the oats, so stop when combined. A frequent error is using the mixer here which can pulverize the chips, losing their character.
Working with 1 heaping tablespoon of dough at a time, roll dough into 1 1/2 inch balls and lay on prepared baking sheets about 2 inches apart: The dough should feel slightly tacky but hold its shape when rolled; you will see flecks of oats and chips in each ball. Proper spacing allows air to circulate and prevents cookies from merging into each other. If the dough is too warm, the balls can flatten prematurely, so chill briefly if needed. Many bakers crowd the sheet and end up with unevenly baked, unevenly shaped cookies.
(I use the OXO medium cookie scoop, a size 40 portioner, and do 12 scoops of dough per baking sheet): Using a scoop creates uniform cookies that bake evenly and look professional on the plate. The metallic click or release feels satisfying and consistent every time. If you eyeball portions, you will get uneven sizes and differing bake times, so a scoop is a worthwhile tool. Avoid overfilling the scoop which creates oversized cookies that may not bake through.
Bake for 7 to 8 minutes for chewy cookies, or 9 to 10 minutes for crispy cookies: You will notice the edges turn a light golden brown and the centers may still look slightly soft and puffy; that is the moment to pull chewy cookies. For crisp cookies, allow the centers to take on a bit more color and firmness. Timing matters because residual heat continues to cook the cookie after removal, so underbaking leaves them unset and overbaking leaves them dry. Do not open the oven repeatedly which causes temperature drops and can ruin texture.
Cool on baking sheets for 2 minutes and transfer to wire racks to cool completely (if you don't let the cookies cool, they may crumble): The cookies will feel firmer at the edges and slightly soft in the center during that brief rest, and transferring to a rack lets air circulate so the bottoms do not steam. Cooling sets the structure and helps the chips solidify back into pleasant morsels. If you try to move them too soon they will break, and if left too long on a hot sheet they can overcook. A common mistake is stacking warm cookies which causes them to stick together.