In a large mixing bowl, cream together brown sugar, white sugar, and butter until light and fluffy.
Mix in eggs one at a time.
Add the sourdough starter and the vanilla extract and mix until thoroughly incorporated.
In a smaller mixing bowl, combine oats, flour, baking soda, salt, cinnamon, and nutmeg.
Add the flour mixture to the wet ingredients. Stir until just combine.
Stir in the chocolate chips.
Cover and chill the cookie dough for 30 minutes to 1 hour.
Preheat the oven to 350° Fahrenheit.
Use a cookie scoop and drop cookies about 3 inches apart onto parchment lined or lightly greased baking sheets. Press each cookie slightly to flatten.
Bake 11 to 12 minutes until edges are lightly browned. The centers should still look soft.
Let the cookies cool on the pans for 5 minutes and then transfer to a wire rack.