Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper or silicone baking mats.
In a medium bowl, whisk together 2 cups of flour, ½ tsp baking soda, ½ tsp salt, and 1 tsp cinnamon. Set the dry ingredients aside while we move on to the wet mixture.
In a large bowl, mix the ¾ cup of melted butter, 1 cup of brown sugar, and ½ cup of granulated sugar. Stir until the sugars are fully dissolved into the butter, and the mixture looks smooth and creamy.
Next, add 1 egg, 1 egg yolk, and 1 tbsp of vanilla extract to the butter-sugar mixture.
Gradually mix the dry ingredients into the wet ingredients, stirring until just combined.
Fold the oats and raisins into the dough until they’re evenly distributed.
Using a cookie scoop or a spoon, drop balls of cookie dough onto the prepared baking sheets. Space them about 2 inches apart to give the cookies room to spread while baking.
Bake the cookies at 350°F for 10-12 minutes, or until the edges are golden brown, but the centers still look slightly underdone
Let the cookies cool on the baking sheets for about 5 minutes before transferring them to a wire rack to cool completely.