Combine the flour, sourdough starter, and milk in a large bowl.
Mix to combine and then cover with cling wrap or something comparable.
Allow the mixture to sit for about 6 hours or until bubbly.
Note: The process will go faster in a warmer environment. I got it down to about 2 hours by putting it in a warm, but not hot oven.
Preheat the oven to 350°.
Spray a Bundt pan with cooking spray and in mixing bowl combine the sugar and melted butter. Beat with an electric mixer for 1-2 minutes.
Add the extracts, salt, and baking soda. Beat to combine.
Continue mixing while adding the eggs, one at a time.
Add this mixture to the bubbly sourdough bowl. Mixing these two together will take some work. I find a wooden spoon or concave spatula work best to force the two to combine.
Once the sourdough pound cake mixture is fully incorporated, pour it into the Bundt pan.
Bake for at 25-30 minutes, until the edges are brown and a toothpick comes out clean when inserted.
Let the sourdough pound cake cool in the Bundt pan for at least 10-15 minutes before attempting to remove it. When the edges of the bake have pulled slightly away from the pan, put a plate on top and flip the whole pan over, shaking lightly to loosen the cake so it falls onto the plate.
Note: If it does not give way easily, allow to cool further. You can also assist the process slightly by running a knife along the outside between the cake and the pan, but be careful not to damage the pan.
Enjoy! Sourdough pound cake is best served warm! Some like to add butter or icing, but my family and I prefer it as is. There is plenty of butter in the cake already and the combination of flavors require no additional topping for us.