1.Preheat oven to 350°F.
2.Cut butter stick in half. Soften at room temperature. Or, place in a microwave-safe bowl. Heat in microwave for 10-15 seconds to soften. Be careful not to melt butter.
3.In a large bowl, blend butter, white sugar, and brown sugar, using a rubber spatula or fork. Mix until light and creamy.
4. Crack egg into bowl. Add milk and vanilla. Mix until smooth.
5.Add flour, salt, and baking soda. Mix until just blended. Do not over mix.
6.Add rolled oats and “mix-ins.” Mix until all ingredients are blended.
7.Lightly coat a baking sheet with non-stick cooking spray.
8.Scoop 1 Tablespoon of dough per cookie. Use your hands to shape dough into a ball. Place 2 inches apart on the baking sheet.
9.Bake until cookies are lightly browned on bottom, about 8-10 minutes. Remove from oven. Let sit 2-3 minutes to firm up before removing from baking sheet. Let cool.
10.Repeat steps 7-9 until all cookies are baked. Cookies may take more or less time to become lightly browned depending on your oven. Watch closely so they do not burn.