Preheat the oven to 325 degrees.
Line 3 cookie sheets with parchment paper and then set them aside.
Place the butter in a small bowl and melt it in the microwave for about 30-60 seconds. Set it aside to cool to room temperature.
Combine the flour, baking soda, and salt in a small bowl – making sure to spoon and level your flour. (please don’t scoop it for these cookies.) Set it aside.
Beat together the melted butter, brown sugar, and granulated sugar in a large mixer bowl.
Add in vanilla, egg, egg yolk and cinnamon, beating 2-3 minutes or until light and creamy.
Slowly stir in the flour mixture, taking care to not overmix. Stir until just combined.
Fold in the oats, raisins, and nuts.
Place large spoonfuls, approx 1/4 cup each onto the prepared cookie sheets, spacing 1-2″ apart.
Add any additional raisins or nuts into the tops of the dough if desired.
Bake 14-16 minutes or until slightly golden brown around the edges but the centers are still slightly soft.
Allow the cookies to cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.
Don’t over-bake. The cookies will set as they cool. You want to keep them chewy.
If you make smaller cookies, please reduce the baking time.