Many oatmeal cookies are dry, cakey, and overly spiced. To make ours dense and chewy, we combine unsaturated fat (vegetable oil) and saturated fat (butter) in a ratio of nearly 3 to 1, and we reduce the proportion of flour. Adding an extra egg yolk boosts moistness and richness, while a touch more salt than most recipes call for tempers the sweetness and complements the oaty flavor. Most recipes call for using a stand mixer, but we found this counterproductive to our goal of chewy, dense cookies because the mixer beats air into the dough. Instead we make our dough by hand, melting the butter for easier mixing. Browning the butter delivers more complexity, and blooming a small amount of cinnamon in the butter rounds out its flavor. Raisins add pops of brightness and reinforce the chewy texture.
Regular old-fashioned rolled oats work best in this recipe. Do not use extra-thick rolled oats, as they will bake up tough in the cookie. For cookies with just the right amount of spread and chew, we strongly recommend that you weigh your ingredients. If you omit the optional raisins, the recipe will yield 18 cookies.
1. Adjust oven rack to middle position and heat oven to 375 degrees. Line 2 rimmed baking sheets with parchment paper. Whisk flour, salt, and baking soda together in medium bowl; set aside.
2. Melt butter in 8-inch skillet over medium-high heat, swirling pan occasionally, until foaming subsides. Continue to cook, stirring and scraping bottom of pan with heat-resistant spatula, until milk solids are dark golden brown and butter has nutty aroma, 1 to 2 minutes. Immediately transfer browned butter to large heatproof bowl, scraping skillet with spatula. Stir in cinnamon.
3. Add brown sugar, granulated sugar, and oil to bowl with butter and whisk until combined. Add egg and yolk and vanilla and whisk until mixture is smooth. Using wooden spoon or spatula, stir in flour mixture until fully combined, about 1 minute. Add oats and raisins, if using, and stir until evenly distributed (mixture will be stiff).
4. Divide dough into 20 portions, each about 3 tablespoons (or use #24 cookie scoop). Arrange dough balls 2 inches apart on prepared sheets, 10 dough balls per sheet. Using your damp hand, press each ball into 2 1/2-inch disk.
5. Bake, 1 sheet at a time, until cookie edges are set and lightly browned and centers are still soft but not wet, 8 to 10 minutes, rotating sheet halfway through baking. Let cookies cool on sheet on wire rack for 5 minutes; using wide metal spatula, transfer cookies to wire rack and let cool completely.