Heat the oven to 325°F (165°C). Line a cookie sheet with parchment paper or a Silpat liner.
In a medium bowl, mix the melted butter, brown sugar, and granulated sugar until well combined.
Add the egg yolk and vanilla extract, and beat until the mixture is creamy. Set aside.
In a small bowl, combine the flour, baking soda, cinnamon, and salt.
Gradually stir the flour mixture into the butter mixture until well mixed.
Fold in the oats and raisins.
Scoop the dough using a medium cookie scoop or a large tablespoon, and place the cookies 2 inches apart on a baking sheet.
Bake for 8 to 10 minutes.
Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a cooling rack to finish cooling.
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Notes
Read Before You Start: Take a moment to read through the entire recipe, including the Ingredient Notes, to ensure you’re set up for success. Every detail is covered in the post.
Measure Flour Correctly: To avoid dense cookies, spoon flour into your dry measuring cup and level it off with a knife. Scooping directly from the container can compact the flour, leading to dry cookies.
Prepare the Cookie Sheet: Line your baking sheet with a silicone mat or parchment paper. Greasing the sheet can cause the cookies to spread too much.
Baking Time Matters: Remove the cookies from the oven as soon as the edges are lightly golden. Overbaking will dry them out, so keep an eye on the timer.
Even Cookie Sizes: Use a cookie scoop (about 2 to 2.5 tablespoons) to portion the dough for consistent cookies. This recipe should make 4-5 cookies.
Easy Swap: Not a fan of raisins? Replace them with the same amount of chocolate chips for a chewy oatmeal chocolate chip cookie variation.