Cream the butter and sugars: In a large mixing bowl, beat the softened butter with brown sugar and granulated sugar until light and fluffy (about 2-3 minutes with an electric mixer).

Add wet ingredients: Beat in the eggs one at a time, followed by the vanilla extract. Make sure each egg is fully incorporated before adding the next.

Combine dry ingredients: In a separate bowl, whisk together the flour, baking soda, cinnamon, and salt.

Mix everything together: Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined. Fold in the oats and any optional add-ins like raisins or chocolate chips.

Chill the dough: Cover the bowl with plastic wrap and refrigerate for at least 30 minutes (or up to 24 hours).

Bake to perfection: Preheat oven to 350°F (175°C). Scoop 2-tablespoon portions of dough onto parchment-lined baking sheets, spacing them about 2 inches apart. Bake for 10-12 minutes until edges are golden but centers still look slightly underdone. Let cool on baking sheet for 5 minutes before transferring to a wire rack.