Beat the softened butter with the brown sugar and granulated sugar on medium speed for about 3 minutes, then add the eggs and mix on high for about 1 minute. Scrape the bowl, then beat in the vanilla and molasses until the mixture looks smooth, glossy, and creamy.
Whisk the flour, baking soda, cinnamon, and salt in a separate bowl, then mix the dry ingredients into the butter mixture on low speed just until no dry streaks remain. Fold in the oats, raisins, and walnuts if using on low speed, and expect a thick, very sticky dough.
Chill the dough in the refrigerator for 30 to 60 minutes, using the full hour when you want to limit spreading. The chilled dough should feel firmer and easier to portion without adding extra flour.
Heat the oven to 350°F (177°C) and line two large baking sheets with parchment paper or silicone baking mats. Cool baking sheets help the dough begin baking at the right pace instead of melting too quickly.
Portion about 2 tablespoons of dough for each cookie, roll into balls, and arrange them 2 inches apart on the prepared sheets. A cookie scoop keeps the portions even and makes the sticky dough much easier to handle.
Bake for 12 to 14 minutes, then leave the cookies on the baking sheets for 5 minutes before moving them to a wire rack. Pull the pans when the sides are lightly browned with a golden ring at the base and the centers still look very soft, because they finish setting on the warm sheet.