Preheat your oven to 350°F and position racks in the upper and lower thirds so you can bake two sheets simultaneously. While the oven heats, measure out all your dry ingredients—flour, baking soda, cinnamon, and salt—into one bowl and whisk them together to distribute the leavening agents evenly. Measure your oats and raisins into separate small bowls. Having everything measured and ready before you start mixing ensures the dough comes together quickly and prevents overmixing.

In a large bowl, beat the softened butter with both the brown sugar and granulated sugar for 2-3 minutes until the mixture is noticeably lighter in color and fluffy. This creaming process incorporates air into the dough, which helps the cookies rise slightly and creates a tender crumb. I prefer using Kerrygold butter here because its rich flavor really shines in these cookies and makes them taste homemade in the best way.

Add the room-temperature eggs one at a time, beating well after each addition, then add the vanilla extract and mix until fully combined. Room-temperature eggs incorporate more smoothly into the butter mixture and create a more homogeneous dough. The batter should look well-blended and slightly fluffy at this point.

Add the dry ingredient mixture from Step 1 to the wet ingredients and stir with a wooden spoon or spatula until just combined—don't overmix. Overmixing develops too much gluten, which makes cookies tough instead of tender. The dough should look slightly shaggy but hold together when you press it.

Gently fold the oats and raisins from Step 1 into the dough using a spatula, stirring just until evenly distributed. I like to slightly crush a handful of the oats before adding them—this helps the cookies bind together better and prevents them from being too crumbly. The dough should be thick, chunky, and studded throughout with oats and raisins.

Drop rounded tablespoon-sized portions of dough onto ungreased baking sheets, spacing them about 2 inches apart since they'll spread slightly. Bake for 8-10 minutes until the edges are set but the centers still look slightly soft—they'll finish cooking as they cool. The cookies should be golden brown around the edges but still pale in the center for optimal texture.

Let the cookies cool on the baking sheet for 1 minute (this allows them to set slightly and firm up for easy transfer), then use a spatula to transfer them to a wire rack to cool completely. This brief rest on the sheet prevents them from breaking apart while still allowing them to finish cooking gently from residual heat.