Heat the oven to 350°F. The oven should be hot before the cookies go in.
Line a baking sheet with parchment paper. This keeps the cookies from sticking.
In a bowl, mix the butter and sugar until smooth and creamy. It should look soft and spreadable.
Stir in the egg until fully mixed. The dough should look thicker and glossy.
Add flour, baking soda, and salt. Mix just until no dry spots remain.
Stir in the oats and chocolate chips. The dough will look chunky and thick.
Scoop dough into large mounds and place them a few inches apart on the baking sheet.
Bake for 10–12 minutes. The edges should be golden, but the centers should still look soft.
Let the cookies cool on the pan for a few minutes before moving them. They will firm up as they rest.