📖 Instructions

1. Before you even think about mixing, make sure your butter is truly softened. This means leaving it out at room temperature for at least an hour, or until you can easily indent it with your finger. If it’s too cold, it won’t cream properly. If it's melted, your cookies will spread too much and be flat. Also, preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper. This parchment paper is a game-changer for even baking and easy cleanup!
2. In your large mixing bowl, the one you'll be using for the wet ingredients, combine the softened unsalted butter, granulated sugar, and packed light brown sugar. Use an electric mixer (either a stand mixer with the paddle attachment or a hand mixer) and beat on medium speed for about 2-3 minutes. You want this mixture to be light and fluffy, almost pale in color. Scrape down the sides of the bowl with a rubber spatula halfway through to ensure everything is incorporated.
3. Now, crack in that large egg and add the vanilla extract to your creamed butter and sugar. Continue beating on medium speed for another minute, until the egg is fully incorporated and the mixture is smooth. Don't worry if it looks a little curdled at first; keep mixing!
4. In a separate, medium-sized bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt. Make sure these dry ingredients are thoroughly combined. The baking soda helps with rise and spread, and the cinnamon is essential for that classic oatmeal cookie flavor.
5. With your mixer on low speed, gradually add the dry ingredients to the wet ingredients. Mix just until *barely* combined. The moment you see no more streaks of flour, stop the mixer! Overmixing develops too much gluten, which can lead to tough cookies, and we're aiming for chewy, remember?
6. Gently fold in the old-fashioned rolled oats and the raisins using your rubber spatula. Mix only until they are evenly distributed throughout the dough. You don't want to crush the oats or overwork the dough.
7. This next step is crucial for that chewy texture and to prevent excessive spreading: chill the dough! Cover the bowl with plastic wrap and refrigerate for at least 30 minutes. If you can chill it for an hour, even better. This allows the butter to firm up again and the flavors to meld. Patience is a virtue, especially when it comes to cookies.
8. Once the dough is chilled, scoop rounded tablespoons of dough onto your prepared baking sheets, leaving about 2 inches between each cookie. A cookie scoop works wonders here for consistent sizing and even baking. You don't want them too close, as they will spread a bit.
9. Bake one sheet at a time in your preheated oven for 10-12 minutes. The edges should be golden brown, but the centers should still look slightly soft and maybe a little puffy. This is the key to chewiness! If they look fully set and golden all over, you've probably overbaked them. Each oven is different, so keep an eye on them starting around the 9-minute mark.
10. As soon as you take the cookies out of the oven, let them cool on the baking sheet for 5 minutes. They are delicate right out of the oven. This allows them to set up a bit. After 5 minutes, carefully transfer the cookies to a wire cooling rack to cool completely. Enjoy with a cold glass of milk, just like Grandma used to serve 'em!