2 sticks (8 ounces) unsalted butter, at room temperature
1 1/4 cups packed dark brown sugar
2 large eggs, at room temperature
2 teaspoons vanilla extract
1/4 cup whole milk
3 cups old-fashioned oats
2/3 cup semisweet chocolate chips
Heat the oven to 350°F and arrange a rack in the middle. Place flour, cinnamon, salt, and baking soda in a medium bowl and whisk to combine.
Place butter and brown sugar in the bowl of a stand mixer fitted with a paddle attachment. Beat on medium high until light in color and fluffy, about 3 minutes. Add eggs and vanilla extract and beat until completely incorporated, about 1 minute. Stop the mixer and scrape down the sides of the bowl.
Add 1/2 of the flour mixture and beat until just incorporated. Add 1/2 of the milk and mix until just incorporated. Continue with remaining flour mixture and milk, mixing until ingredients are just incorporated and smooth. Remove the bowl from the mixer and stir in oats and chocolate chips.
Drop dough by level tablespoons onto a baking sheet, spaced 1 inch apart. Bake until golden brown on the edges, about 11 to 12 minutes. Immediately transfer cookies to a wire rack and let cool completely.