Start by preheating your oven to 350°F (175°C). A warm oven is essential for that ideal texture.
In a medium bowl, whisk together the flour, baking soda, baking powder, salt, and cinnamon. This step is crucial as it ensures that all the leavening agents and spices are evenly distributed throughout the flour.
In a large bowl, cream the softened butter, granulated sugar, and dark brown sugar together until light and fluffy. This should take about 2-3 minutes with an electric mixer. The result should be creamy and slightly pale.
Beat in the two large eggs one at a time. Make sure each egg is fully incorporated before adding the next. Then, mix in the vanilla extract. That signature vanilla aroma will start to fill your kitchen at this point!
Gradually add the dry mixture to the wet mixture, stirring carefully until just combined. Be cautious not to over-mix. Your dough should be thick and luscious.
Fold in the rolled oats, plump raisins, and chopped walnuts or pecans. Make sure everything is well-coated with the dough. You want to ensure that every cookie has an even distribution of goodies in each bite.
Using a cookie scoop or tablespoon, drop dollops of dough onto a baking sheet lined with parchment paper. Leave space between each cookie; they will spread while baking.
Place the baking sheet in the preheated oven and bake for 10-12 minutes, or until the edges are golden brown. The centers may look slightly underbaked, but they will firm up as they cool.
Allow the cookies to cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely. Enjoy with a glass of milk or your favorite beverage!