Chewy, thick, and delicious, these are very easy cookies with a great caramel flavor from those butterscotch chips (or chunks, even better). They can be out of the oven in less than 30 minutes, or you can keep the dough in the refrigerator for a couple of days.
Preheat the oven to 350ºF (180ºC). Line cookie sheets with parchment paper or butter the pans.
Beat soft ¾ cup unsalted butter with 1 cup brown sugar and ½ cup white sugar in a large bowl 2 minutes, until smooth.
Add 1 egg and 1 teaspoon vanilla extract, and beat for 3 minutes.
Add 3 cups old-fashioned rolled oats, 1 ¼ cups all-purpose flour, ½ teaspoon baking soda (sift it to avoid lumps), and ¼ teaspoon salt. Mix just until incorporated.
Add 2 tablespoons milk and mix until well incorporated. Add 1 cup butterscotch chips or morsels and mix well.
Bake them immediately or refrigerate the batter for 1 hour and up to a day. See Notes below.
Scoop walnut-sized balls (I use a small cookie scoop, 1,57-inch diameter) on the prepared sheets, leaving space between them, about an inch and a half. If using refrigerated dough, flatten slightly on top.
Bake for 10 to 12 minutes, until golden and beginning to firm around the edges, but the center is still soft. If you want crunchier cookies, bake them for a minute or two more.
Cool for a few minutes on a wire rack before lifting them carefully from the paper and cooling them completely.
Keep in tins, cookie jars, or airtight containers.
Notes
Baking time: Keep in mind that all ovens and pans are different, even if they look the same or very similar. The baking time in my recipes is as accurate as it can be, but it might take you more or less time. You can use an oven thermometer to check that your oven is at the right temperature. I recommend tracking how your oven works and what tiny details you might need to adjust.Measuring the cookies: Use an ice cream or cookie scoop so that your cookies bake evenly. Leave roughly a 1 or 2-inch separation between each (depending on the size), so they can spread comfortably during baking.Refrigerating the dough:I don't chill it and bake the cookies directly. The texture is fantastic. But the type of oats you use might differ from mine as they can vary depending on what part of the world you live in and what brand you buy. You should not have issues with quick-cooking oats because they hydrate quickly. With rolled oats, I recommend you test a few cookies first and see how they come out. Letting the dough rest from 1 hour to a day might help to make moister and softer cookies. The oats will soften with the extra hydration time. Baking: if making the cookies immediately, scoop and bake. If the cookie dough has been refrigerated for several hours to a day, it will be firmer, even after it comes to room temperature. Lightly press the top of each cookie before baking. When the dough is stiff, the cookies don't spread as much. Batching and freezing: Make a large batch (double this recipe, for example) and freeze them (I pop the baking sheet with the scooped-out cookies in the freezer and then transfer them to a bag when they are rock solid). It will save you time and always have freshly baked oatmeal cookies. You can consult a post dedicated to freezer baking. Butterscotch chips or chunks: I love using both, and if you can't get chunks, you can use the Dulcey chocolate from Valrhona, chopped. Variation: These also work great with white chocolate or vanilla chips. You can make a large batch, divide it and make different cookies simultaneously.