Set the butter out to allow it to come to room temperature and preheat your oven to 350° F.
Mix the wet ingredients
In a large bowl, cream the butter and sugar with an electric mixer for 2 minutes. (This whips air into it and gives your cookie more structure).
Add the plant milk and vanilla and mix on low for about 30 more seconds until you have a light fluffy mixture.
Mix in the dry ingredients
Add flour, baking soda, baking powder, salt, and cinnamon and mix on low for about 1 minute until all ingredients are combined.
Pour in the oatmeal 1 cup at a time, mixing between each cup.
Stir in your choice of raisins, chocolate chips, or anything else that you would like in your cookies.
Use a cookie scoop to spoon 1 tbsp of cookie dough balls onto an oiled cookie sheet (or line it with parchment paper).
Bake the cookies
Bake at 350° F for 11 minutes. (They will still look a little doughy in the middle).
Take out of the oven and allow to cool on the cookie sheet for about 5 minutes before moving to a flat surface to cool the rest of the way.
Store in an airtight container.
Notes
Bake for 11 minutes. They will most likely still look doughy in the center, but take them out anyway. They will firm up and become chewy.
Cooking for more than the recommended 11 minutes will make them more brittle and crispy.
Spray your cookie sheet will a little oil (or rub a thin layer of oil on it) to avoid sticking.
Allow the cookies to cool on the cookie sheet for about 5 minutes before transferring them.
Place the cookies on a flat surface to cool completely.
Don't add too much to the cookies. About 1/2 cup of raisins, chocolate chips, or nuts is enough to add flavor. If you add too much, you won't have enough dough to hold them together.