Preheat your oven to 350°F (175°C). Prepare your baking sheets by lining them with parchment paper or silicone mats. This will prevent the cookies from sticking and make cleanup a breeze.

In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until the mixture is light and fluffy. This should take about 3-4 minutes. The creaming process is crucial as it incorporates air into the butter, which helps to create a light and tender cookie.

Beat in the eggs, one at a time, ensuring each is fully incorporated before adding the next. Stir in the vanilla extract. The eggs add moisture and help bind the ingredients together, while the vanilla adds a touch of aromatic sweetness.

In a separate bowl, whisk together the flour, baking soda, cinnamon, and salt. This ensures that all the dry ingredients are evenly distributed, preventing pockets of baking soda or cinnamon from forming.

Gradually add the dry ingredients to the wet mixture, mixing just until combined to avoid overworking the dough. Overmixing can lead to tough cookies, so mix just until you see no streaks of flour.

Gently fold in the rolled oats, dried cranberries, and chopped walnuts until evenly distributed. This step is where the dough comes to life with texture and flavor.

Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart to allow for spreading. Uniformity in size ensures even baking.

Bake in the preheated oven for 10-12 minutes, or until the edges are golden and the centers are set. The cookies will continue to firm up as they cool, so don't worry if they look slightly underdone in the center.

Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely. This brief rest on the baking sheet allows the cookies to set, making them easier to handle.