Soak the raisins in warm water for 10 minutes to plump them up, then drain well and set aside. If using walnuts, ensure they're toasted and chopped. Bring the butter to room temperature (around 70°F)—this is crucial for proper creaming and incorporation of air into the dough. Measure out all dry ingredients (flour, baking soda, cinnamon, salt) and have them ready near your mixing station.

In a large mixing bowl, combine the softened butter, packed brown sugar, and granulated sugar. Beat on medium speed for about 2 minutes until the mixture is light, fluffy, and pale in color. This creaming process incorporates air into the dough, which helps the cookies rise and develop a tender crumb. I like to use a stand mixer for this step because it ensures even incorporation without overmixing later.

Add the eggs one at a time to the creamed butter mixture from Step 2, mixing on medium speed for about 1 minute total to fully incorporate them. Then add the molasses and vanilla extract, mixing until everything is well combined and the batter is homogeneous. The molasses adds depth and moisture to the cookies, so make sure it's fully incorporated throughout the mixture.

In a separate bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt. Whisking instead of just stirring ensures the leavening agent (baking soda) is evenly distributed throughout the flour, which helps the cookies rise uniformly. I prefer to use freshly ground cinnamon for noticeably better flavor compared to pre-ground.

Add the dry ingredient mixture from Step 4 to the wet mixture from Step 3, stirring on low speed just until combined—don't overmix or the cookies will be tough. Once the flour is incorporated, add the old-fashioned rolled oats, drained raisins from Step 1, and chopped walnuts (if using). Mix on low speed until everything is evenly distributed throughout the dough. The oats should be evenly dispersed so every cookie has plenty of texture and flavor.

Transfer the dough to the refrigerator and chill for 30 to 60 minutes. Chilling allows the flavors to meld and makes the dough easier to handle when scooping and shaping. While the dough chills, preheat your oven to 350°F and line your baking sheets with parchment paper so everything is ready when you're done chilling.

Remove the chilled dough from the refrigerator and roll it into 1-inch balls, placing them about 2 inches apart on the prepared baking sheets. Bake at 350°F for 12 to 14 minutes, until the edges are golden brown but the centers still appear slightly underdone—they'll continue cooking on the hot baking sheet. Remove the cookies from the oven and let them cool on the baking sheets for 5 minutes to set slightly before transferring to a wire rack. This resting period prevents them from breaking apart while still maintaining a soft, chewy center.