Cream together: In a large mixing bowl, cream the softened unsalted butter and both sugars until fluffy and light, approximately 4 minutes.

Add wet ingredients: Incorporate the large egg and vanilla extract into the butter mixture. Mix well until everything is nicely blended and smooth.

Combine dry ingredients: Gradually add the old-fashioned rolled oats, all-purpose flour, cinnamon, baking soda, and optional pinch of salt. Mix until just combined.

Fold in chocolate: Gently fold in the heaping cup of semi-sweet chocolate chips and any optional mix-ins.

Chill the dough: Form the cookie dough into 11 to 12 equal mounds on a baking sheet. Flatten slightly and chill for at least 2 hours.

Preheat and prepare: Preheat the oven to 350°F (175°C) while lining your baking sheets with parchment paper.

Bake cookies: Bake in the preheated oven for about 11 minutes or until the edges are set and centers remain slightly glossy.

Cool and enjoy: Allow cookies to cool on the baking sheet for 10 minutes, then transfer them to a wire rack.