In a large bowl, use an electric mixer to beat the softened butter, brown sugar, and granulated sugar together until light and fluffy—about 2 to 3 minutes.
Add the eggs one at a time, mixing until fully incorporated. Then mix in the vanilla extract and milk.
Gradually stir in the rolled oats until evenly combined with the wet mixture.
In a separate bowl, whisk together the flour, baking soda, and salt.
Slowly add the dry ingredients to the oat mixture, mixing just until combined.
Fold in the chocolate chips by hand to evenly distribute them without overmixing.
Cover the bowl and refrigerate the dough for at least 1 to 2 hours, or up to 2 days. If too firm when removing from the fridge, let it sit at room temperature until scoopable.
Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper or silicone baking mats.
Using a 4-teaspoon spring-loaded scoop (or about 1½ tablespoons), drop dough balls onto the baking sheets, leaving about 2 inches between each.
Bake for 10 to 12 minutes, or until the edges are lightly browned but the centers still look soft.
Let the cookies cool on the baking sheets for 5 minutes, then transfer them to wire racks to cool completely.