In a large mixing bowl or stand mixer, cream butter and sugars together until fluffy and light in color--about 3-5 minutes. Add the eggs and vanilla and beat until well combined.
Stir the dry ingredients in the wet ingredients until just combined.
Add in mix-ins to batter (either all at once or divide dough into different bowls and add in different mixtures for each batch of dough.)
Refrigerate dough for at least 30 minutes.
Preheat oven to 375 degrees F.
Using a tablespoon for each cookie, roll into a ball.
Bake for 6-7 minutes, until edges are lightly browning and centers are still a bit jiggly. Cool on cookie sheet for a minute or two before transferring to a cooling rack.
For Oatmeal Chocolate Chip Cookies
Mix in 2-3 cups chocolate chip into batter before refrigerating.
For Coconut Oatmeal Chocolate Chip Cookies
Mix in 1 cup semi-sweet chocolate chips, 1 cup shredded coconut and 1 cup chopped almonds (optional) into the cookie batter before refrigerating.
For Cranberry White Chocolate Oatmeal Cookies
Mix in 2 cups dried cranberries, 1 cup white chocolate morsels and 1 teaspoon orange zest into the cookie batter before refrigerating.
For Oatmeal Raisin Cookies
Mix in 2 cups raisins, 1 teaspoon cinnamon, and up to 1 cup chopped walnuts (optional) into the cookie batter before refrigerating.
This recipe calls for 2 1/2 cups of blended oatmeal. To blend your oats, place oats into your blender and whirl away until a powdery substance forms. The important part of this is to measure the oats AFTER you blend them, not before–baking is a science.